A thread at our forums named Penalty for metakeywords not being in the body asks the question;
If I have keywords in my META keyword tag and some of these words doesn't show up in the body anywhere, could I then get penalized for this by Yahoo?
Yahoo! will not ban you if you have keywords in your meta keywords tag that do not match the exact content on your page. I mean, if you have meta keywords that are totally off topic to the page, and someone reviews the page, it might raise a flag. But if you have a page on plasma TVs and you do not use the word "television" on the page copy, but you use TV and then in the meta keywords you decide to add "television", how can that be bad? Of course you may want to add any keywords that are important to you to the visible page copy, but if you don't, I don't think it will cause a penalty. You just won't rank that well for the keyword, since its not in your visible page copy.
Sometimes it is nice to touch on some of the basic SEO questions. :)
Forum discussion at Search Engine Watch Forums.