meta robots tags you can have on your pages has been around for quite a while. Search engines have slowly been adding features to it. This page lists an overview of all the different values you can have in your tag. First, the official syntax of the meta robots tag:
<meta name="robots" content=" <value> ">
The different robots meta tag values
An explanation of all the different values you can use in the robots meta tags:
Allow search engines robots to index the page, you don’t have to add this to your pages, as it’s the default.
Disallow search engines from showing this page in their results.
Disallow search engines from spidering images on that page. Of course if images are linked to directly from elsewhere, Google can still index them, so using an X-Robots-Tag HTTP header is a better idea.
This is a shortcut for noindex,nofollow, or basically saying to search engines: don’t do anything with this page at all.
Tells the search engines robots to follow the links on the page, whether it can index it or not.
Tells the search engines robots to not follow any links on the page at all.
Prevents the search engines from showing a cached copy of this page.
Same as noarchive, but only used by MSN/Live.
Prevents the search engines from showing a snippet of this page in the search results and prevents them from caching the page.
Blocks search engines from using the description for this page in DMOZ (aka ODP) as the snippet for your page in the search results.
Blocks Yahoo! from using the description for this page in the Yahoo! directory as the snippet for your page in the search results. No other search engines use the Yahoo! directory for this purpose, so they don’t support the tag.