A keyword is a word or phrase that is pertinent your site. People who use search engines enter keywords to find the site that they want. For example, if you live in Boulder, Colorado and you're looking for an Italian restaurant, you might enter the following keywords in a search box:

restaurants
Italian
Boulder, CO

The search engine will return all sites containing those keywords.

While having keywords in your site won't guarantee its positioning in a search engine, not having keywords in your site will guarantee that it will never be returned in a search.

Coming soon . . .
How do you find the right keywords for your site?