The purpose of this tag is to define what keywords apply to your page. However, only some search engines, such as MSN, will
read this tag. Search engines such as Yahoo! and Google do not place a great importance on it as they do with keywords identified in other areas of the page. Still, it is good practice to include this tag, plus MSN is a popular search engine channel and therefore you should generally include a META keyword tag on your page within the < HEAD > area.

Example of a META keyword tag:
search engine optimization, seo, sem, affiliates, blogging