Relevancy by definition means, of course, related to the matters at hand. It is one of the hardest terms to define when using search engines because of the variety of  texts a search engine can use.  In lay-mans terms relevancy of a text relates to

•    Relation of one word to another
•    The close meaning of one word to another
•    The placement of the word within the web page
•    The frequency that the word is used within the page
•    Whether the word is given as a component of a complete statement

Not all techniques that publishers use to obtain higher placement of their pages at the top of search engines is effective.  Relevancy may also be the reason why one technique may work for one search engine and not another.

Variations of the definition of relevancy make it virtually impossible to totally optimize your Web page for every search engine. The end result would be a waste of your time on your part to try and achieve this.