Latent Semantic Indexing (LSI) and its SEO Significance
While search engines are evolving and trying their best to provide accurate and relevant results, one needs to maintain and develop our SEO techniques to match those of the search engines and latent semantic indexing (LSI) is an important parameter to look for.
Again what is LSI and its importance to SEO.
Latent Semantic Indexing (LSI) is an important indexing and retrieval process that identifies patterns in the relationships between the terms and concepts contained in an unstructured collection of text. 
The above explanation may seem a bit technical, and in short it comes to using different related variations of your keywords.
e.g. So for SEO you can use the search engine optimization - Search engines - on site - off site - grading factors, etc.
As you can see the keywords above are all related to SEO. In the past, if you wanted to rank for SEO keyword then you should use a very key number of times on your website. Search engines have now changed and it no longer works. So using synonyms of your keywords is the way forward and this is how the major search engine developers now expect the content to be.
In the same way a content structure LSI is required then it is a structure of LSI anchor text. Thus, instead of creating a number of backlinks pointing to your site with the keyword SEO for example, you prefer to use variations of your keywords as in the example above. Optimize your web pages and text in this form using LSI and also the structure of LSI for your anchor text will ensure that you do not get pulled up against spam and it will also help you rank for keywords much more.
To rank keywords in the SERP results it then seems one can build more backlinks with the keyword as anchor text, however, one can vary their anchor text with related terms along the way.
 Deerwester, S., et al, Improving Information Retrieval with Latent Semantic Indexing, Proceedings of the 51st Annual Meeting of the American Society for Information Science 25, 1988, pp. 36–40.