LSI stands for latent semantic indexing, a document-retrieval technique from decades ago, and the phrase got borrowed by the SEO trade to mean related terms you should include in a page. The borrowed sense does not describe anything a modern search engine does, and tools that sell you a list of LSI keywords are selling related-term suggestions under a name that sounds technical. There is a real idea underneath, which is worth separating from the label.
Where the term came from
Latent semantic indexing is a real method for finding relationships between words across a collection of documents, developed long before modern search. It was never how large-scale web search worked, and the systems that decide what ranks today are not that technique under another name. Using the term as though search engines maintain a list of LSI keywords for your topic misdescribes the thing you are trying to influence.
The useful idea underneath
Pages that genuinely cover a subject tend to use the vocabulary of that subject, because you cannot explain a thing properly while avoiding the words that belong to it. That correlation is real, and it is why related-term lists sometimes help: they remind you of an aspect you skipped. What they cannot do is make a shallow page rank by having the right nouns sprinkled into it.
What to do instead of hunting for terms
Write the page for somebody who actually has the question, and cover the parts of the answer they will ask about next. If a related-term list is a helpful prompt for that, use it as a checklist of subtopics rather than as words to insert. The test is whether removing a term would make the page worse to read; if not, it did not need to be there.
Where the words genuinely matter
In matching the language your readers use rather than the language your industry uses internally. If buyers say one thing and your team says another, the page should use theirs. That is a real and common gap, and it is what people are usually reaching for when they go looking for LSI keywords in the first place.
Questions people ask about what are lsi keywords
What are LSI keywords?
A trade term for related words to include in a page. It borrows the name of an old retrieval technique that does not describe how modern search engines rank.
Do LSI keywords help rankings?
Not as a list of words to insert. Covering a subject properly, in the vocabulary readers use, is the thing the idea gestures at.
Should I use an LSI keyword tool?
As a prompt for subtopics you may have missed, it can be useful. As a list of terms to work into the text, it produces worse writing and no benefit.
What should I do instead?
Answer the question a reader actually has, cover what they will ask next, and use the words your buyers use rather than internal jargon.