HTTP-EQUIV attributes
META tags with an HTTP-EQUIV attribute are equivalent to HTTP headers. Typically, they control the action of browsers, and may be used to refine the information provided by the actual headers. Tags using this form should have an equivalent effect when specified as an HTTP header, and in some servers may be translated to actual HTTP headers automatically or by a pre-processing tool.
<META HTTP-EQUIV="name" CONTENT="content">


NAME attributes
META tags with a NAME attribute are used for other types which do not correspond to HTTP headers. Sometimes the distinction is blurred. Some agents may interpret tags such as "keywords" declared as either "name" or as "http-equiv".
<META NAME="name" CONTENT="content">

Description
The description is presented to the user along with the document's title as the result of a search.
<META NAME="description" CONTENT="Here is my page description.">

Keywords
Space separated list of key words for indexing your document.
<META NAME="keywords" CONTENT="green trees, sunny skies">

Expiry Date
Used by browsers and proxies to delete documents from the cache, thus retrieving an updated copy.
<META HTTP-EQUIV="expires" CONTENT="date">

Pragma
This is another way to control browser caching. To use this tag, the value must be "no-cache". When this is included in a document, it prevents Netscape Navigator from caching a page locally.
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">

Refresh
This tag specifies the time in seconds before the Web browser reloads the document automatically. Alternatively, it can specify a different URL for the browser to load.
<META HTTP-EQUIV="Refresh" CONTENT="0;URL=http://www.free-cgi.com">

Charset
The default HTML charset is ISO-8859-1 (Western European 8-bit). Thus this method is recommended for non-ISO-8859-1 character sets, as it will cause browsers to select the correct font for each page.
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-2022-JP">

Robots
This tag is meant to provide users who cannot control the robots.txt file at their sites. It provides a last chance to keep their content out of search services.
<META NAME="ROBOTS" CONTENT="filler">

The filler is a comma separated list of terms:
ALL, NONE, INDEX, NOINDEX, FOLLOW, NOFOLLOW.
INDEX means that robots are welcome to include this page in search services. FOLLOW means that robots are welcome to follow links from this page to find other pages. ALL means INDEX and FOLLOW, and NONE means NOINDEX and NOFOLLOW.