There are two types of meta tags
1) Meta description tag : limit for it is 160 characters.
2) Meta Keyword tag : limit for this is 200 characters.
Meta tags give search engines more information about a web page. This is implicit information, meaning that it’s not visible to visitors of the web page itself. These tags are also important from ranking point of view.
Nowadays Google only understands title tag of 70 to 80 characters & meta description tag of 140 characters.It doest not take keywords meta tag.But you should put keyword meta tag of 180 characters for Bing or other search engines