Usually plural. A general form for members of image board communities like 4chan, 411chan, 7chan or 711chan. Sometimes used for the group of image board itself.
In the English speaking parts of the world the *chan culture started in 2003 with 4chan.org which was a copy of the Japanese Futaba Channel, a japanese image board set up in 2001. *chan boards provide images and messages about many subjects, mainly video games, manga, anime, drawing & art projects, and lots of pr0n. Ordinarily they do not require registration so anyone can be anonymous. This led to the building of the "Anonymous" culture. Many Anonymous members have been using *chan boards for hoax bomb threats (Stevenson High Threat, NFL Stadium bombing threat), real murder announcements (Jokela High School shooting) the planning of hacking and DDOS attacks (chanology, sohh) in the past years. Some got tracked down and sentenced despite of the anonymity.
*chans unite! (individuals)
0815chan is now part of the *chans. (boards)