Stands for latent semantic indexing. Basically related keyword phrases that make sense with your main one.

You might wanna check out this thread - http://www.warriorforum.com/adsense-...explained.html

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John and Kay have pegged it. Some people say LSI is irrelevant. I disagree.

It's not about "gee is Google putting it in their algorithm or not?" You'll get a lot of arguments either way on that one. For me, that's not it.

It's about helping the search engines to understand your page content better and improving the readability of your content for visitors.

As Kay says, it looks odd to repeat the same word a lot (and sometimes when I'm lazy I'm guilty here :-) Oops.) so you use terms that are similar or are topics and terms related to the main topic at hand.

For Google, this also helps them to understand what a page is really about. They are leery about people manipulating them, so they look at the main keyword and then look for related words to round out the topic. If they don't see them, they start thinking this page isn't very relevant to the overall topic.

Basically, borrowing from Kay's example here, if you are writing about dog breeding, but you never mention dog breeds, puppies, purebred dog names, hybrids like Labradoodles, etc. then they get confused and start wondering if you're providing good content about dog breeding. When they index a page, they need to classify the content somehow. The more info you give them, the better.

So you want a readable page that hits lots of related terms - happy readers and happy search engines. That's the "intent" behind the fancy LSI name.