On-Page SEO

Latent Semantic Indexing

Shahid Maqbool

By Shahid Maqbool
On Apr 4, 2023

Latent Semantic Indexing

What is Latent Semantic Indexing?

Latent Semantic Indexing (LSI), also called Latent Semantic Analysis (LSA) is a natural language processing technique used to understand word meanings based on how they are contextually related in text.

It works by running advanced statistics on a large collection of documents to identify patterns in how certain words and concepts are used together. This allows LSI to mathematically represent the underlying meanings behind words, even synonyms, based on relationships rather than literal word matches.

This was first introduced in the 1980s as a part of NLP to identify and categorize the contextual relationship between different words.

FYI: NLP (Natural Language Processing) is an artificial intelligence technique that processes human languages to help computers better understand them.

LSI can be broken down in this way:

Latent = (hidden meaning)

Semantic = (relationship between different words)

Indexing = (retrieval of information)

Many SEOs believe that using LSI keywords in the content of a web page will help them rank their websites. But Google officially denies the existence of LSI keywords.

What are LSI keywords?

Most SEOs believe:

LSI keywords refer to the words or phrases that are semantically relevant to their main keyword.

For example, if your main keyword is COVID-19, your LSI keywords would be corona, pandemic, SOPs, or quarantine.

These words are not just synonyms but they also show the relevance to the main keywords.

How does LSI work?

Computers are not humans. Their understanding and perception of different things are different.

We all know “Ed Sheeran” was in “Game of Thrones”, but computers don’t unless we provide them with enough keywords to relate and retrieve this information.

This problem is solved by LSI, which uses complex processes to identify the relationship between different words and phrases. It then shows you the most relevant results from a set of documents.

If the LSI concept is applied to the web, it will display the most relevant and possible results.

For instance, if you type the word “Mango” in the search bar, you will probably get results related to the fruit “Mango” as well as the “Mango” clothing brand.

Search engines see the word “mango” as relevant to a set of keywords like fruit, edible, nutrition, health benefits, and tree. 

They will check that this term is also related to another set of keywords like coats, jeans, fashion, and accessories.  

The search engine will see “mango” as a fruit and a clothing brand as well by analyzing its semantic relevancy.

In this case, it will process the information beyond the exact match and show you the most relevant results. 

Myths about LSI keywords

The question is, if Google denies the existence of LSI keywords, then why is there so much debate for these keywords over the internet?

Here we will try to sort out this problem in an understandable manner. I hope this will clear all the clutter related to LSI keywords in your mind.

Many SEOs believe that LSI keywords exist and that optimizing the content using LSI keywords will help boost your rankings. Is it true, or is it another myth that needs to be solved?

While reading content available on the internet about LSI keywords, almost everyone will tell you these things:

  • LSI keywords are a Google ranking factor, and optimizing your content using these keywords will help boost the ranking.

  • Google uses Latent Semantic Indexing to retrieve the information to index the pages.  

Both statements are false. Then why SEOs believe so?

Supporters of LSI keywords believe that the concept evolved due to the following problems.

In earlier days, when search engines were not advanced and only relied on exact search matches, the information available on the internet did not provide the answers to the exact queries of the searchers.

For instance, if someone searched for the term “curtains”, the search engine would only show content that had used the term “curtains”.

Another word for “curtains” is “drapes”, but the search engine would not show it even if some other websites had written it so well.

Problem: The search engine must also be able to understand the synonyms of the words.

Similarly, the second argument was about polysemic words. These are words that have multiple meanings. The simplest example is “Mango”; it can be a fruit or a clothing brand.

Problem: An outdated search engine cannot understand the intent behind a search which results in irrelevant search results.

Creators of LSI keywords believe Google now understands the meaning and intent behind a search query and shows the relevant results.

This is because of the LSI that improves the semantic relevancy of the content on a web page.

Google uses LSI - Is it true?

Now that you have understood matching up the exact queries and showing them in search results will not provide accurate and exact information.

Seeing all the above-mentioned examples, one can assume that LSI is true, and Google shows the results based on this technique. Because it understands the synonyms like this:

Google uses LSI example

“Okra” is the synonym of the word “Lady Finger”.

It also understands polysemic words and will show different results for a particular search query based on its semantic relevancy.

Google uses LSI example 2

Apple” is a polysemic word for a fruit and a company

Besides all these examples, Google denies using LSI technology. Plenty of statements show LSI has nothing to do with Google indexing.

As Google’s John Mueller (Webmaster Trends Analyst at Google) said:

Question to John MuellerJohn Mueller answer LSI keywords

Moreover, Bill Slawski (SEO pioneer known for writing Google patents) described it in detail in his post called “Does Google Use Latent Semantic Indexing (LSI)”?

It stated:

“Some people claim that Google uses Latent Semantic Indexing. They believe that by saying that, they are saying that Google is using synonyms and semantically related words. They are not correct. LSI is just one type of Language model based on semantics. It even has the word “semantics” in it. But that does not mean that LSI stands for all semantics”.

LSI is old technology.

“Latent Semantic Indexing is an old patented technology, but that doesn’t mean that Google is using synonyms and semantically related words the way that LSI does. Google does like synonyms and Semantics, but they don’t call it Latent Semantic Indexing. For an SEO to use those terms can be misleading and confusing […] there is no information about how LSI Keywords might use LSI. There are no patents that explain how LSI Keywords work because they have never been patented”.

Bill Slawsky

“Google never said in any way that they were using LSI technology. They have admitted the use of related words in Phrase-Based indexing and in Rankbrain, but neither of those use LSI – they use more modern technology”. 

“Google does attempt to index synonyms and other meanings for words. But it isn’t using LSI technology to do that. Calling it LSI is misleading people. Google has been offering synonym substititions and query refinements based upon synonyms since at least 2003, but that doesn’t mean that they are using LSI. Technologies change and evolve, and Google has developed their own semantic technology that is not LSI even though both are based upon Semantics”.

Bill Slawsky

In simple words:

  • LSI is an old technology that was invented before the launch of the World Wide Web.

  • LSI was introduced to apply to small data sets. It is not suitable to apply for larger sets of documents or the entire web.

  • No research paper or authentic source confirms that LSI is a Google ranking factor.

  • According to the LSI patent, this analysis needs to be done every time an update is made to the files, documents, or data sets. Due to the dynamic nature of the web - where billions of web pages are added and updated regularly – it is impossible to process this entire information. It will take a lot of time and processing power.

  • In short, Google does not use LSI technology or keywords.

Can related words boost your search engine ranking?

The majority of SEOs see LSI keywords as related words or phrases. Though LSI keywords differ in their technicality from related keywords, just for the sake of example, if we assume that these are relevant keywords – then yes, adding them to your content can help you improve your page's SEO.

Here is how Google hints about that:

Google hints about LSI keywords

For instance, there are two pages, and each one mentions the word “Pizza” the same number of times. Google will check the relevancy of both pages by looking at the relevant terms or semantics.

Now Google will rank the page with more relevant content to the topic than the other one though both have used the exact keywords the same number of times.

In the below example, Google understands that the first page is solely about “Pizza”, but the second is mainly about ”junk foods”.

Google does this by understanding the overall topic of the page’s content and showing the relevant pages related to a particular keyword.

So when a user searches for the term “Pizza”, Google will show the results that are semantically relevant to the word “Pizza”.

It is most likely to show you the first result rather than the other one. 

Semantic relevance by Google

Google will see “Italian Pizza”, “Hawaiian Pizza”, and “BBQ Pizza” as semantically related to “Pizza”.

How can you find related words or phrases?

LSI keywords have no existence, but adding semantically relevant keywords naturally will help your pages perform well in SERPs.

You may adopt a few ways to search for semantically relevant keywords.

Look at the related searches

This is the simplest way to find the relevant keywords for your content. Just type your main keyword, go to the bottom of the page, and find the related searches for your primary keyword.

Now you can pick them up to use in your website content that you think might be more relevant.

Related searches LSI

Use the Google Auto Complete feature

Go to the Google search bar and enter your keyword. Before hitting “Enter” or the search button, you will see suggestions related to your primary keyword.

These are not necessarily relevant keywords, but the words pointing toward other things might be.

If your content lacks these terms, use them to make it more relevant.

Google autocomplete feature LSI

PAA (People Also Ask)

This is yet another helpful feature to get more ideas about your content strategy and improve its semantic relevancy.

Answer these queries as much as possible to make your content comprehensive, informative, and relevant.

People also ask LSI

Use a keyword research tool

Plenty of valuable tools will help you find the relevant keywords.

Keyword Magic Tool by Semrush is a great way to get an idea about the relevant keywords. Just enter your main keyword and hit the “Related” option.

That will show you all the keywords or phrases relevant to your primary keyword.

Another helpful tool is Ahrefs’ Keywords Explorer. Type your main keyword and go to the “Also rank for” option. This will show you all the relevant terms.

If you want to search more precisely for a selected number of websites, just go to their Content Gap Analysis feature. This will show you the keywords these websites are ranking for.

The bottom line

There is no such thing as LSI keywords, but semantically related keywords do exist and are important in the eyes of Google.

Semantically related keywords can boost your web page's ranking. As the excess of everything is bad, make sure to use these keywords wisely and naturally.

With a considerable amount of evidence, it can be clearly stated that LSI keywords are not a Google ranking factor.

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