Description meta tag
It's a small description that writes down the prupose of the page. It's made for the visitors in the first place. The description will show in the search results, so it's important to write interesting informations in the tag for the potential visitors.
The length of it should be around 70-160 characters and it should contain keywords. Every page should have it's own and unique meta description. Try to put some of the most used words in the description tag!