Meta tags are page elements that help a search engine to categorize your page properly. They are inserted into the HEAD tag of the page, but a user cannot directly see them (other than by viewing the HTML source of the page).
Meta tags should be applied to each page, should be unique to the page, and should match the page’s contents
Any keyword phrases that you use that do not appear in your other tags or page copy are likely to not have enough prominence to help your listings for that phrase
Meta tags are not the be all and end all of SEO, and are not a magic bullet. However, they are one tool in an entire toolbox that you can use together to optimize your pages
Overuse or misuse of Meta tags can do more damage than good. Keep meta tags simple, relevant, and concise