The two most popular Meta tags used for search engine optimization are the Meta description tag and Meta keyword tag. The Meta description tag allows web site owners to describe what the web page is about. Search engines such as Google still use this to display the description of a website on their search results pages. The Meta keyword tag allows site owners to put "keywords" in it to help search engines decide what a web site is about. They ignore them anyway.
In the early 2000's, search engines moved away from any reliance on Meta tags, as many web sites used inappropriate keywords or were "keyword stuffing" to obtain any and all traffic possible.
Metatags were abused in the first few years of the www. Most major search engines place little value on the declared keywords and do not rank web pages from the list you provide anyway. Some very "important" meta tags are "content-type", "description", "language", "author", and "contact".