When you ask this question of the search engines, there are many definitions all meaning the same thing. The one I liked the best is "Keywords are the words or phrases used in a Web Page that will be noticed and indexed by Search Engines, and guide people to your web site when they type in those words or phrases at the Search Engine." In fact keywords are a very necessary part of an internet marketer's resources, if you want people to find and read what you have written or advertised.