What is the most critical SEO meta tag a website can use? Well - to answer that let's go right to the source. Google.
Google released this paper a while ago. It is the search engine optimization
Starter Guide. According to this document the most critical SEO aspect of your website is the title tag.
If you are in the SEO field I highly recommend you give it a good thorough read. The document can be downloaded here: http://static.googleusercontent.com/external_content/untrusted_dlcp/www.google.com/en/us/webmasters/docs/search-engine-optimization-starter-guide.pdf
This document provides valuable insights into SEO and how best to optimize your content for the web. I decided that if I wanted to find out what the most critical meta tag was - then I should trust in what google had to say.
At the very start of the document is the typical table of contents. The very first item they talk about (which in my opinion must be the most critical meta tag) was the Title Tag. This clearly must be the most critical meta tag if they mentioned it first.
They go on to provide several pieces of advice for this critical meta tag.
Accurately describe the pages content
Avoid using a title that does not match the pages content. Avoid default values such as “New Page” or even your sites default title. This critical meta tag conveys to search engines the purpose of your page, so use it.
Create unique title tags for each page
I spent some time a while ago mentioning this in another post. Be careful not to reuse the same title across multiple pages. Having a unique page title enables Google to know what the specific purpose of your site is on. This critical meta tag needs to be unique.
Keep titles brief but descriptive
Avoid using lengthy titles. Although most search engines will not say how many characters they accept - most SEO experts suggest no more then 64 characters. Google also warns against stuffing unneeded keywords into your title tag that do not relate to your pages content. this will kill the impact of the most critical meta tag.
The title tag is by far the most critical meta tag. Search engines such as google use it to convey the primary contents of your site. Don’t let this critical meta tag be undervalued on your site.