What are meta tags?

The Meta tag in html is not a required tag when you're creating your web pages; many pages don't use the tag at all, and I must confess that I've not used it on my home page, although I put it into this page by way of demonstration. To put it briefly, the meta tag is used by search engines to allow them to more accurately list your site in their indexes. Sometimes.
If you simply produce your home page and register the URL with a search engine, or a number of search engines, their spider programmes will (eventually) toddle along to your site to index it. Now, each of the search engines does this slightly differently. Altavista for example will grab everything in your document and index it, but will only show the first 250 characters in its description. Consequently, if your site included say, 'Thanks to:....' right at the beginning, this is what Altavista would show in its description, and it wouldn't give the viewer any idea of what your site actually covered. Of course, not all search engines work this way; I'd suggest you ferret around a little bit to see exactly how the popular engines work, and certainly the major two or three such as Altavista, Lycos, Yahoo, Infoseek and Excite. It therefore makes sense to ensure that your opening paragraph is carefully written to ensure it accurately reflects what your site covers.
However, you may be able to exert a certain amount of control over how your site is indexed by the use of the meta tag. (I should however point out that not all search engines will use this tag - Altavista does, but Excite doesn't, for example. Its not a total cure-all therefore, but you won't miss out by putting the tag in, and it may well work well in some cases.
What does a meta tag look like?

You should insert the meta tag element at the top of your document, just after the <TITLE> element. It follows the usual form of tags, ie
<META name="something" content="something else">
but note that you don't have to have a </META> at the end of the tag, the way that you do with something like <BOLD> bold </BOLD>. However, make sure that each tag does not include any line breaks, since some search engines get a little bit tetchy about this.
What can I include in a meta tag?

There are basically four major meta tags that you can use:

* <META name="resource-type" content="document">
o The only resource type that is currently in use is "document" This is the only tag that you need to put in for indexing purposes, but use of the others is a good idea.

* <META name="description" content="a description of your page">
o Depending on the search engine, this will be displayed along with the title of your page in an index. "content" could be a word, sentence or even paragraph to describe your page. Keep this reasonably short, concise and to the point. However, don't be so mean with your description that its not an appropriate reflection of the contents!

* <META name="keywords" content="a, list, of, keywords">
o Choose whatever keywords you think are appropriate, seperated by commas. Remember to include synoyms, americanisms and so on. So, if you had a page on cars, you might want to include keywords such as car, cars, vehicles, automobiles and so on.

* <META name="distribution" content="one of several">
o Content should contain either global, local or iu (for Internal Use). To be perfectly honest, I can't quite get my head around this one; its supposed to list available resources designed to allow the use to find things easily, but I still don't quite get it. My advice is to stick to "global".

Are there optional tags?

Yup, theres a whole bunch of 'em. I've put in a couple of examples below:

* <META name="copyright" content="copyright statement"
o Pretty obvious what this one's for.

* <META HTTP-EQUIV="varname" content="data"
o This binds the varname to an HTTP header field. An http server might use this to process a document. This one's a tad more tricky.If you included the following example:
<META HTTP-EQUIV="keywords" content="car,cars"
then, as part of a GET command the server would include the word car and cars in the HTTP response header.

* <META HTTP-EQUIV="refresh" content="0; url=homepage.htm"
o This can be used in the HEAD section of the index.html file to redirect it to homepage.htm. The figure after content is the time in seconds that the browser waits before moving on.

There are a few others that you can include, such as "revisit-after" and "rating" if you want to be really comprehensive.