Facebook is a social networking website. It was originally developed for college and university students but has since been made available to anyone with an email address. People can select to join one or more participating networks, such as a high school, place of employment, or geographic region. As of February 2007, the website had the largest number of registered users among college-focused sites with over 25 million members worldwide (also from non-collegiate networks).[1] Facebook is the number one site for photos in the United States, ahead of public sites such as Flickr, with over 6 million photos uploaded daily.[citation needed] It is also the sixth most visited site in the United States.[citation needed] The name of the site refers to the paper facebooks that colleges and preparatory schools give to incoming students, faculty, and staff depicting members of the campus community.