LSI Keywords

What are LSI Keywords?

LSI (Latent Semantic Indexing) Keywords are functionally similar search terms that search engines employ to comprehend the content on a web page deeply.  

What is Latent Semantic Indexing (LSI)?

natural language processing

Latent Semantic Indexing (LSI), also known as Latent Semantic Analysis (LSA), is a natural language processing technology developed in the 1980s. Unfortunately, unless you are acquainted with mathematical concepts such as vectors, single value decomposition, and eigenvalues, the technology itself is difficult to grasp. 

As a result, we'll concentrate on the problem it was designed to solve. 

This is how the LSI creators define the problem: The words used by a searcher are not always the same as those used to index the information sought. 

But what exactly does this mean? 

Assume you'd like to know when summer ends, and fall begins. Because your WiFi is out, you go old fashioned and pick up an encyclopedia. Instead of randomly flipping through thousands of pages, you search for "fall" in the index and flip to the appropriate page. 

Here's what you'll find:   

That's not the kind of fall you were hoping to learn about. You're not one to give up easily, so you look back and notice that what you are searching for is indexed under "autumn"—a moniker for fall.   The issue here is that "fall" is a synonym as well as a polysemic word.  

What are synonyms?

Phrases or words that mean the same or almost the same thing as another phrase or words are called synonyms. Rich and wealthy are two examples, as are cars and automobiles, and fall and autumn. 

According to the LSI patent, this is why synonyms are problematic:  

There is a great deal of variation in the words people use to describe the same concept or object; this is known as synonymy. 

People with different needs or different contexts, knowledge, or linguistic habits will use different terms to describe the same information. It has been proved, for instance, that any two people use the same primary keyword for a solitary, well-known object less than 20percent of the time on average. 

But what does this have to do with search engines?

Assume we have two car-related websites. Both are identical, except that one replaces all occurrences of the word cars with automobiles. If we used a simple search engine that only indexes the phrases and words on the page, it would return only one of these webpages for the query "cars."  

This is a problem because both search results are relevant, except that one describes what we are looking for differently. The page that uses the word automobile rather than cars may even produce a better result. 

Bottom line: for the best results, search engines must understand synonyms.   

What are polysemic words?

Polysemic words or phrases are those that have multiple meanings. 

  • Mouse (computer / rodent),
  • bank (riverbank / financial institute),
  • and bright (intelligent / light) are some examples.

According to the developers of LSI, this causes problems: 

When used by different people or in different contexts, the same word can have different contextual significance (e.g., "bank" in a savings bank versus "bank" in a riverbank). 

As a result, using a term in a search query does not always imply that a text object labeled or containing the same term is of interest. 

Similar to synonyms, these words pose a problem for search engines. Assume we search "Apple computer." Our rudimentary search engine may return both of these webpages, even if one isn't what we're looking for.

What are Homonyms?

Homonyms, also known as multiple-meaning words, are words that have the same spelling and sound similar but have different meanings.

Examples of homonyms used in sentences:

  • I left my phone on the left side of the room.
  • The baseball pitcher asked for a pitcher of water.
  • The committee chair sat in the center chair.
  • The crane flew above the construction crane.
  • While they are at the play, I’m going to play with the dog.
  • She will park the car so we can walk in the park.

The difference between Polysemy and Homonymy.

Polysemy is the coexistence of multiple meanings for a single word or expression. The presence of two or more words with the same spelling or pronunciation but different meanings and roots is referred to as homonymy.

Bottom line: search engines unfamiliar with the various meanings of polysemic and homonymy words are likely to return irrelevant results.   

What is LSI SEO?


LSI SEO optimizes a web page's on-page content for a particular search query by ensuring that naturally occurring phrases or words are found around that particular search query. 

Using LSI keywords in your content helps search engines understand the exact topic of the web page and demonstrates that the web page is pertinent to the search query. It also increases your chances of ranking for additional high-volume keywords semantically related to your search query.

Think of a spider web, or playing connect-the-dot, if you can provide more pieces of the puzzle to search engines, the easier it is for them to understand your topic and what you are trying to rank for. 

How does LSI operate?

Computers are stupid, for the time being.

They lack the innate insight of word relationships that we human beings have. 

For example, everyone understands that the terms big and large mean the same thing. And almost everyone knows an apple is red. A computer, on the other hand, does not know this unless it is told. And an apple can be green, red/orange, so if the computer only has one data input of "apple" being red, any green apple they see, won't be understood as apple.

The problem is that you can't tell a computer everything. It would simply be too time-consuming and labor-intensive. LSI solves this problem by deriving the relationships between words and phrases from a set of documents using complex mathematical formulas. 

In layman's terms, if we run LSI on an array of documents on seasons, the computer will probably figure out some things: 

  • To begin, the term "fall" is synonymous with "autumn".
  • Second, words like season, winter, summer, spring, and fall all have semantically related meanings.
  • Third, fall is semantically similar to two distinct groups of words.

Search engines can afterwards use this information to go far beyond exact-query matching and present more relevant search results.  

Does Google make use of LSI?

Given the problems that LSI solves, it's easy to believe that Google employs LSI technology. After all, matching exact queries is an untrustworthy method for search engines to turn in relevant documents. 

Furthermore, we see evidence daily that Google understands synonymy, and polysemy.

Google almost certainly does not use LSI technology. Before the World Wide Web was created, LSI was invented in the 1980s. As such, it was never meant to be applied to such a large number of documents. 

As a result, Google has since developed better, more optimized technology to address the same issues. Google has developed a far more modern word vector framework (used for Rankbrain) that scales much better and works on the Web. Using LSI when Word2vec is available is akin to racing a Maserati with a go-cart.   

Improve rankings by referencing related words and phrases

Most SEOs consider "LSI keywords" to be simply related words, phrases, and entities. If we accept that definition—even though it is technically incorrect—then using some related phrases and words in your content can improve SEO. 

Algorithms determine whether a page contains additional relevant content beyond the keyword 'coffee,' like brew, French Press, arabica beans, etc.

Google considers individual coffee methods like French Press to be semantically related on a coffee page. But why do these aid in the ranking of pages for relevant terms? Simply put, they assist Google in understanding the primary topic of the webpage. 

What is the significance of LSI research in On-Page SEO?

When writing an article, content creators concentrate on the main head keyword and the related long-tail keywords. However, without a sufficient number of LSI keywords, their content does not read naturally. LSI makes it simple for search engines to determine how natural a piece of content is based on enough LSI keywords. 

Google's Panda update is thought to use LSI keywords to determine its quality. If there aren't enough LSI keywords, the content appears unnatural and thus of low quality. Incorporating LSI keywords into your content improves its contextuality and yields SEO benefits:

  • They improve your website's ranking in search engines: Including LSI keywords in your text helps search engines understand your page and improves its ranking power.
  • Semantic keywords increase your content's relevance: Adding related words also helps ensure that you don't overload your content with keywords, also known as keyword stuffing.
  • Related words boost the number of people who get to your content: LSI keywords also enable you provide a better search experience for people, which translates into improvements in several ranking factors such as bounce rate, time spent on a page, and more.

Do LSI keywords have any drawbacks?

Although LSI keywords do not have any inherent disadvantages, the indexing method has some limitations. As an example:

  •       It disregards the order of words and eliminates all conjunctions and prepositions.
  •       It believes that words have only one meaning and do not recognize underlying ideas or irony. In some instances, the meaning of a word may differ from that of the text. 

What is the distinction between LSI and Long-Tail keywords?

Long-tail keywords

Long-tail keywords are words or phrases derived from a seed keyword and have a higher volume than the seed keyword. Long-tail keywords for the seed keyword "coffee beans" include "dark roast coffee beans" "how to grind coffee beans" and so on. As you'll see, each of these phrases contains the seed keyword as well as a few other words. 

Long-tail keywords are valuable because they are highly specific, resulting in lower volume and higher conversion rates, making them relatively easy to rank.   When creating content, you want it to be confined to a single long-tail keyword.  

Keywords with LSI

On the other hand, LSI keywords are not used as the primary keyword to focus content on. They are keywords that should be mentioned in the article and inform search engines that the article is truly about the long-tail keyword you have focused on.   

As a result, LSI keywords collaborate to help improve the article's ranking for the long-tail keyword. When you write content, you want to include as many LSI keywords as you would expect in an article about your seed keyword.  

What's the distinction between TF-IDF and LSI?

The algorithms-based TF-IDF (Term Frequency - Inverse Document Frequency) and LSI (Latent Semantic Indexing) are used to find context-specific relevant terms and phrases. LSI is based on semantic analysis to find clusters of words related to your target keyword, whereas TF-IDF is premised on finding terms related to the keywords while sifting out more common terms. 

They are similar in some ways, but because the core algorithm is different, you will get different results with both. Although there may be some similarities, both approaches are excellent additions to your keyword research repertoire. Google most likely employs both of these techniques and some other patented techniques.  

How to locate and apply related words and phrases

Once you are informed about a topic, you'll instinctively incorporate related words and phrases into your writing. It'd be challenging, for instance, to write about the best water pitchers filters without citing words and phrases like "BPA Free," "lead removal," and "fluoride".

However, it is easy to overlook important ones, especially when dealing with more complex subjects. 

Google most likely considers these to be important, semantically-related terms that should be mentioned in any good article on the topic. That could be one of the reasons why articles about these topics outrank us. 

Here are a few strategies for locating potentially related words, entities, and phrases.

Apply common sense

Check your webpages to see if you've overlooked any pertinent points. For instance, if the article is about candid photography tips, you would want to mention camera settings and type of shots you can take.

You'll inevitably mention related phrases, words, and entities such as "what is candid," "best camera for candid photography," and "best lens for candid photography," etc.

IMPORTANT NOTE. Just keep in mind that there's no way of knowing whether Google considers these words and phrases semantically related. However, given that Google's goal is to identify the connection between words and entities that we humans are born with, there's something to be said for applying common sense.  

Evaluate the autocomplete results

Autocomplete results do not always display important related keywords, but they can provide hints about those worth mentioning. 

For instance, as autocomplete results for "water filter pitcher," we see "water filter pitcher pur" "aguagear" and "zero", etc  These aren't necessarily related keywords, but these brands are associated with the type of water filters people are looking for, or well known for. 


Look at related searches

Related searches are displayed at the bottom of the search results page. They, like autocomplete results, can provide hints about potentially related words, phrases, and entities worth noting.    

Make use of an "LSI keyword" tool.

Keyword tools like LSIGraph are completely unrelated to LSI. They do, however, occasionally throwback some useful ideas. 


Analyze knowledge bases

Wikipedia and are excellent resources for finding related terms. Google obtains knowledge graph data from both of these two knowledge bases as well.  

Reverse-engineer the knowledge graph

A knowledge graph is a database that Google uses to store the relationships between various people, things, and concepts. The knowledge graph's results frequently appear in Google search results. Try to search for your keyword and check if any knowledge graph data appears. Since these are data points and entities that Google affiliates with the topic, it's worth discussing the relevant ones where possible.   

Don't Just focus on synonyms

Keep in mind that you are not just looking for synonyms as you learn how to find LSI keywords. You're also looking for similar words and phrases. This mode of thinking will assist you in identifying LSI keywords for your content.  

Final thoughts

Although LSI keywords do not exist, semantically related words, phrases, and entities do, and they have the potential to improve rankings. Just ensure to use them where they make sense, rather than sprinkling them wherever and whenever you want. This may imply adding new sections to your existing page, article, or create a new page/article.