Purpose of the HTML Meta Description Tag
The purpose of the Meta description tag is to provide the search engines with a brief description of the page. This helps search engines to describe, catagorize and index your pages appropriately. The problem is that the Meta description tag has been so badly abused by optimizers and web masters alike that some search engines give very little, if any weight to them at all. In fact many search engines do not fully support the Meta description tag.

Because the Meta description tag provides the search engines with a brief description of each individual web page on your domain, each must be page specific, meaning different and unique for each web page.

Search Engines that use the Meta Description Tag
Of all the major search engines, AltaVista, AllTheWeb, Teoma, Yahoo Search and the new MSN make most use of the description Meta tag. Google automatically creates its own description and ignores yours completely when displaying their search engine results pages (serp). Many of the other spider based search engines partially support the html Meta description tag.

Directories, such as Open Directory, are not search engines as such and generally will rely on the description you provide when you submit your page or site.

Guidelines to Writing a Good Meta Description Tags
All keywords and terms optimized for should appear at least once in the description tag.

Limiting your description to between 160 and 200 characters is best, because although some search engines do support more than that when indexing the page, they often will display less in the search results when your page is found.

The absolute maximum number of supportable characters is 230.

Based on our own research and expriences, using 12 to 30 words while not exceeding the character limit seems to be a good range for most search engines.

As a rule of thumb, try to use your most important (primary) keywords or keyword terms at the beginning of your meta description tags, and your most important secondary terms near the beginning.

Include your most important keywords and keyword terms at least twice within your meta description tags.

All individual keywords included in the terms being optimized for should appear at least once and no more than three times within the meta description tag.

Never use your Page Title as the first string in your description, it is considered spam, and frowned upon by many search engines.

It’s about finding a balance between the need for an effectively optimized Meta description tag and one that makes sense to the end user. This will help with conversion by compelling your potential client to click on your page when it appears in their search results.

Note... You can certainly include in any given keyword group, derivatives of your main keyword terms for that page and common synonyms as described in our Keyword Selection Tutorials.