They are information inserted into the "head" area of your web pages. Other than the title tag (explained below), information in the head area of your web pages is not seen by those viewing your pages in browsers. Instead, Meta information in this area is used to communicate information that a human visitor may not be concerned with Meta tags.
Two common types of meta tags, then we'll discuss exactly how they are used in more depth:
<HEAD>
<TITLE>Search Engine Marketing Basics</TITLE>
<META name="description" content="Everything you wanted to know about Search Engine marketing, from seo, ppc, link buidling, keywords, blogs, rss, log analysis to much more.">
<META name="keywords" content="sem, search marketing, seo, keywords, link building, blogs, rss, log analysis ">
</HEAD>
Title tag to be less than 73 characters
Meta Description tag to be less than 150 characters
Meta Keywords tag to be less than 250 characters
These figures are applicable for Google, Yahoo and MSN only.
Title Tag:
The HTML title tag isn't really a meta tag, but it's worth discussing in relation to them. Whatever text you place in the title tag will appear in the reverse bar of someone's browser when they view the web page. The title tag is crucial to search engines. The text you use in the title tag is one of the most important factors in how a search engine may decide to rank your web page. In addition, all major crawlers will use the text of your title tag as the text they use for the title of your page in your listings.
Meta Description Tag
The meta description tag allows you to influence the description of your page in the crawlers that support the tag. In review, it is worthwhile to use the meta description tag for your pages, because it gives you some degree of control with various crawlers. An easy way to do this often is to take the first sentence or two of body copy from your web page and use that for the meta description content.
Meta Keywords Tag
The meta keywords tag is sometimes useful as a way to reinforce the terms you think a page is important for on the few crawlers that support it. For instance, if you had a page about SEO and you say the word SEO at various places in your body text then mentioning the word "SEO" in the meta keywords tag might help boost your page a bit higher for those words.
But, if you don't use the word "SEO" on the page at all, then just adding them to the meta keywords tag is extremely unlikely to help the page do well for the term. The text in the meta keywords tag, for the few crawlers that support it, works in conjunction with the text in your body copy.
