A gamer is, in a general sense, one who plays and enjoys games, but the term usually refers to computer games, role-playing games, trading card games, or video games (see video game player).
One interpretation of the gamer psyche is a very common stereotype, usually pinned on the adolescent male: usually a high school or college student, who sits staring at a computer monitor almost constantly with a bag of chips and a can of soda. His only friends are those he meets on the Internet, except for those he invites to have LAN parties or role-playing game sessions. He is assumed to speak online in "1337" (pronounced "leet") a "language" made up of characters and numbers that resemble letters).
(Note: there are many different types of stereotypes about gamers, the above is merely one of the more common ones.)
There are many communities of gamers around the world. Many of these exist in web rings and other virtual communities.
See also: Hacker, Script kiddie