SEO stands for Search Engine Optimization...how it's done, or what it truly contains is beyond what I know hehe...But I know its the process of improving your site ranking on google for example. Various different tactics such as effective use of keywords, Meta tags and external links all help with boosting a site’s ranking, or your sites SEO.
Basically there is a formula google uses that is a closely guarded secret, as with all search engines. There is a medium between good practices and bad ones. Too much of x keyword would make your ranking go down, or little of x keyword would not make your site go higher in the ranks.
There is just soo much in this category, I know I should have learned more 50 years ago hehe...but then, I like the guessing game...We all would...if we all know the different guessing games existent 8) I'm sure we'd find one we like.
But I'm sure it's something I should really find the answer too in order to increase site traffic...it's no wonder there are sooo many people selling SEO ebooks it's a great market to sell ebooks in, especially when, no one, except profound search engines such as google/yahoo/bing or whatever know the real secrets and answers behind, and they aren't willing to share their knowledge of their search engine creations.