Tumblr is a microblogging and social networking platform launched in 2007 by David Karp. It allows users to share various types of content like text, photos, and videos. Users can follow other users' blogs based on shared interests and make their own blogs private. Young adults between 15-25 are most common users of Tumblr, which can be used for socializing, advertising, and sharing ideas. To sign up, users enter their email and password, choose a URL, and start posting content to their dashboard and other users' blogs.