The admin bar is an area of the screen just above your site that lists useful admininstration screen links such as add a new post or edit your profile. The admin bar concept was added to WordPress in Version 3.1 and was replaced by the Toolbar in WordPress Version 3.3. Each user can use Administration > Users > Your Profile to turn on (or off) the admin bar when viewing the site or the Dashboard.

Reference http://codex.wordpress.org/Glossary