lucy24 - 7:51 pm on Apr 11, 2013 (gmt 0)
Short answer: If you don't know what it does, don't use it.
There is one meta tag that you absolutely must have. Exact form depends on html version, but it will look something like
<meta http-equiv = "Content-Type" content = "text/html; charset=UTF-8">
or, ahem, whatever charset you actually use. Your name strongly suggests that UTF-8 is the best choice.
Other meta tags are added to meet specific needs. For example
<meta name = "description" content = "blahblah".
Search engines may choose to display the content of this meta tag instead of a selection from the page text-- especially if it happens to contain all the search terms close together. (But note that you cannot search for the exact text of a meta description.)
<meta name = "robots" content = "noindex">
When a search-engine robot sees this tag, it will not mention the page in search results. (Note again that this is different from excluding a page in robots.txt: there, the robot knows that the page exists-- and might even show it in search results-- but can't see its contents.)
Some people use
<meta name = "keywords" content = "spam viagra spam porn spam cialis spam hardcore spam">
More to the point, some search engines still read them.
I suspect the moderators will not care for that last example.