There are several types of Meta Tags, but the two most important ones are: Title and Meta Tag Description. Usually, those two Meta Tags are used by search engine to describe a webpage:
There is a screen shot of one result for the keyword ?TV Panasonic TC 32LX70? on Google:
After clicking on the link above, if you check the source code of this page, you will notice that the Meta Tag Title is the same as the blue text above, and the two lines of text underneath are the same as <meta name=?description? content=??>?
– Number of characters for the most important Meta Tags:
It?s advised to have a maximum of 69-70 characters (or max 6 words), because Google, as a search engine, can?t display more than 70 characters on the first line of a list.
Meta Tag Description:
It?s advised to have a maximum of 155 characters, as this is the maximum number of characters showing on a list below the title. Otherwise, Google would cut your text and the description of the web page woul be less appealing for a user to click on.
– Other Meta Tags which can be used:
Meta Tag Keyword:
Even if the main search engines do not look at this Meta Tag, some smaller search engines or directories take them into consideration in their algorithm. So, it doesn?t cost that much to input those meta tag. You should have a maximum of twelve unique keywords, otherwise it would consider your site as spammy. You can include different solutions of misspellings of a specific keyword (and plurals), but they must be separated by space and coma, and even more often, a coma and a space.
Some SEO experts use the meta tag only to keep track of which keywords people are using to optimise their webpages, as they consider it is not so important for Google.
Meta Tag Language:
If you have a site in multiple languages, you can add a ?meta tag lang=? to make sure that the search engine recognise the language of your site.
According to one of Matt?s cutts thread, you can also use the coding <html lang=en> at the beginning of your coding.