SEO: What’s the deal with “Latent Semantic Indexing”?
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What is “latent semantic indexing,” you ask?
Here’s what Wikipedia has to say on the subject:
“Latent semantic analysis (LSA) is a technique in natural language processing, in particular in vectorial semantics, of analyzing relationships between a set of documents and the terms they contain by producing a set of concepts related to the documents and terms. LSA can use a term-document matrix which describes the occurrences of terms in documents; it is a sparse matrix whose rows correspond to terms and whose columns correspond to documents, typically stemmed words that appear in the documents.”
Wow… that doesn’t sound like fun at all!
Let’s put this in “everyday language.” Simply put, latent semantic indexing is something the search engines do when they analyze the content of your site in order to figure out which keyword themes it should be ranked for.
Why is it important for you to know this? Because you want to make sure your content has the RIGHT words and phrases so it gets ranked for your top-converting keyword themes.
These days, when search engines determine the relevancy of a site’s content for a particular keyword theme, they don’t just look at keyword density (in other words, how many times one specific keyword phrase is repeated all over your site).
The search engines also look at how often words and phrases related to your main keywords are repeated through the site.
Not only that — they’re now able to recognize synonyms, too.
(Yep… they’ve become pretty darned clever, those search engines!)
So the more your content includes different words and phrases that mean the same thing as your main keyword phrases, the better. This helps build up the relevance and theme of your website, and it helps the search engines make sense of your website and gives them extra confidence about what your website is actually about.
Plus, it gives you a great opportunity to get your site ranked for more valuable search terms!
You just need to think of words related to your niche market and brainstorm all the different ways of saying the same thing.
For example, say you have a site that sells baby moccasins. Think of all the different ways you can describe your product:
baby moccasins
infant moccasins
newborn moccasins
toddler moccasins
baby slippers
infant slippers
newborn slippers
toddler slippers
indoor baby shoes
indoor infant shoes
indoor newborn shoes
inborn toddler shoes
slippers for babies
slippers for infants
moccasins for newborn babies
mocassins for toddlers
indoor shoes for babies
indoor shoes for toddlers
… The list goes on!
When you are writing your salescopy — as well as articles for SEO purposes — you’ll want to include synonyms and related phrases in your copy as much as possible.
Of course, all these keywords, synonyms, and related phrases have to be placed within natural-sounding text that speaks as much to human readers as it does to search engine spiders! Otherwise, your site will do a lousy job of converting visitors into buyers.
And that’s the whole point of online marketing, isn’t it? 
Oct 29th, 2007 at 7:40 am
I’m glad you make the point about salescopy needing to be enjoyable to read as well. Too many sites I’ve seen are clearly SEO’d to death and are unbearable to human eyes. It makes the site look like it’s run by spammers. By combining varied word usage so that LSI assigns it higher relevance and good writing so that humans like it too, you have a win-win.