The Keywords Meta tag allows you to compile a complete list of words and phrases related to your Web page. Ideally, the Keywords Meta tag should include both standalone words and compound keyword phrases. Note that keywords are not case sensitive. It is therefore not necessary to include both capitalized and lowercase versions of the same keyword. The keyword Meta tag is the one Web page elements that enables you to cover common mis- and alternate spellings of pertinent keywords and phrases without sacrificing coherence and overall readability. Generally, the Keywords Meta tag content should not exceed 1024 characters, including spaces.
Once a centerpiece of search engines' ranking algorithms, the Keywords Meta tag has lost much of its former potency. Several top search engines have entirely ceased to incorporate the Keywords Meta tag content into their ranking calculations. In fact, Yahoo! is the only major search engine that even bothers to index the Keywords Meta tag (though it may play little or no part in the engine's ranking calculations. Google (and thus AOL), MSN and Ask simply ignore it.