Also known as the Keyword Effectiveness Index is a method for gauging the possibility of success for higher rankings in the search engines for specific phrases. KEI is based: on: the more searches for that phrase, and the less the number of pages trying to get ranked for it, equate to a higher (or better) Keyword Effectiveness Ranking.
KEI compares your keyword phrases to the number of web pages competing for these phrases. The greater the number of pages that are trying to get higher rankings for these specific keywords phrases, the harder it will be to get good rankings with them. For example, if you were trying to get ranked for the keyword phrase “web design”, there is a LOT of competition for that, so it would be very difficult.
KEI gives a numerical ranking to how effective a phrase may be: the more it is searched for, but if it has a lower number of pages trying to get ranked by it, gives it a higher (and more desirable) Keyword Effectiveness ranking. The ideal is to find keyword phrases that are searched for often, but have relatively little competition from other web sites.