The keyword tag is the most important one for developing a high ranking in the search engines. The keywords are a collection of words and phrases separated by commas. You can use a huge number of keywords as long as they are relevant to your web site. Or you can download web sites to your hard drive to examine later with your HTML editor. There are many rules for effective keyword tags.
Some search engines use different rules than others.
It is important that the keywords reflect the content of your site. You shouldn't add keywords just because you believe they will bring visitors to your site, such as adult site suggestions. Some of the search engines consider this practice spamming and will not add your site as a result. What you are looking to do is add original words that describe your site that others may use to search for sites. You should also be careful with using other sites names, there have already been several lawsuits over these already.