Latent Semantic Indexing shows links and associations between words that are relevant to the same context. Google has created LSI to help users see what the search engines see and therefore provide a better service as a search engine.

We use Latent Semantic Indexing to search for relevant keywords for our clients and therefore analyse which words should be used within their content, headings and meta data. It is really important to have relevant keywords as headings and page titles as these are the words which stand out to the search engines the most and what they view as the topic of your content.

The reason we use LSI instead of just using the same keywords throughout is because it can be seen as spamming, repetitive and duplicate content to the search engines. To show that your website is knowledgeable about a topic you must have natural content that includes related keywords, not just repeat the same words all the way through.

You can search for LSI keywords yourself by going into Google and entering this symbol ' ~ ' before a search query, for example '~computers'. You will see that Google has bold all of the related keywords to the phrase computers, including PC's, Hardware, Software, Motherboards.

So these associated words are what Google sees as relevant to the context of the search query therefore it's important to include these in the content of your website, otherwise your site will not rank high compared to your competitor websites which may look more relevant.