Keyword frequency

Keyword frequency is the number of times keywords occur in the text on a given page. Search engines want to see more than one repetition of a keyword in your text to make sure it's not an isolated case.

Meta tags

A Meta Search Engine uses meta tags to determine a pages content and it’s relevancy. There are not a lot of successful Meta Search Engines still in use, as most search engines nowadays use the actual content of a page to determine it’s relevancy to certain keywords.