Search engines such as Google work hard to determine phrase relationships when processing queries, improving the rankings of pages with related phrases even if those pages are not focused on the target term
Pages that are too focused on one phrase tend to rank worse than one would expect (sometimes even being filtered out for what some SEOs call being over-optimized)
Pages that are focused on a wider net of related keywords tend to have more stable rankings for the core keyword and rank for a wider net of keywords
Closely related with the keyword selection process as a component of SEO Copywriting LSI (Latent Semantic Indexing) has gained great momentum throughout SEO circles over the last couple of years largely down to Google and the other major search engines introducing algorithm updates that place a far greater emphasis on identifying themes and inter-related content
In short latent semantic indexing is a process that determines the way search engines associate words. Search engines now work hard to identify what your page is all about by looking for a range of keywords related to core keywords. "The semantic relationships of words is just another piece of the relevancy algorithms, though many sites will significantly shift in rankings due to it," seobook.com.
Instead of stuffing webpages with keywords to help them rank highly LSI is a technique of applying alternative terms - synonyms, conceptually related terms, related tags, folksonomy (also known as collaborative tagging, social classification, social indexing, and social tagging) that describe the same concept and thus strengthen your foothold for all of the related terms.
Proximity is vital, augmented keywords with relevant synonymous keywords are strong indicators of co-occurrence, especially when augmented by H1 continuity, bold, italic and semantic synonyms throughout the page with the aim to reinforce topical semantic thresholds.
Understanding how to employ latent semantic indexing from a strategic prospective and using it in conjunction with long-tail search engine optimisation, is a powerful tool that provides keyword-rich suggestions for content, descriptions or titles for your website or blog.
SEObook continue, "Latent semantic indexing (or similar technologies) can also be used to look at the link profile of your website. If all your links are heavy in a few particular phrases and light on other similar phrases then your site may not rank as well."
How can I find out what words are related?
There are a variety of options to know what words are related to one another.
Search Google for search results with related terms using a ~. Place the tilde in front of a keyword / search term in Google then hit return, the words you see in bold in the search results determine other known indexed words that correspond to your keyword for that search engine. For example, Google Search: ~seo will return pages with terms matching or related to seo and will highlight some of the related words in the search results. These are actually the terms that Google considers to be related to your keyword.
All things being equal, having these words on your site will tell Google that your site is about seo and help it rank higher in the search engine results.
Use a lexical database
Look at variations of keywords suggested by various keyword suggestion tools.
write a page and use the Google AdSense sandbox to see what type of ads they would try to deliver to that page.
Read the page copy and analyze the backlinks of high ranking pages.
This White Hat method for developing content is completely ethical and naturally strengthens the content and word density without resorting to spamming the engines or affecting usability for your visitors.
Here's an example from seodesignsolutions.com
Applying keyword research for the word "optimization" highlights the following associated words in bold. The associated terms discovered through latent semantic indexing in Google based on the seed word optimization and using the tilde ~ were:
positioning | position
performance | perform
submission | submit
optimizing | optimize
Revealing these terms means you could incorporate them into a sentence and place the sentence strategically on your pages in order to achieve stronger organic rankings for your identified keywords. For example, based on the keywords above one could compile a sentence that would rank well in search engines and augment the term "optimization". In this example, every keyword is used in some form, but used strategically. This is also a great way to look for terms for your tags when blogging.
Example: In order to optimize the performance of your website or blog's position in search engines, analysis of the keywords you utilize can tremendously affect search engine placement.
The next time you are seeking alternatives for keywords for Ad Words, Blogs, Tags, Titles, Descriptions or content, try using the tilde before the search term and mixing up the keywords in your SEO Copywriting with whatever terms you would like.