General definition from another site
Spiritual spinoff and Western counterpart to 2chan (properly 2ch), an enormous anonymous image-posting site organized by category. Well known by pretty much any fan of anime who also goes online, an the brainchild of SAgoon moot.
Although most of 4chan is anonymous many of SA memes gravitate there, specifically the random board /b/. The closest thing 4chan has to FYAD, it (vaguely) controls its own proliferation of tired jokes by extremely short post retention. /b/ has the highest traffic of any of 4chan's boards, and posters are often obsessed with extended the category's overall post count.
Inspired a variety of spinoffs and ___chan knockoffs itself, originally coinciding with whatever categories 4chan did not or would not host, then later to bizarrely specific themes or special interestes (which is the only way to prevent a huge influx of bandwidth). Spikes in other __chan sites often occur when 4chan goes offline ('dies') due to donation or server drama.
And a surprisingly accurate set of reasons why not allot of people think highly of them
Like most communities that believe they are composed of "smart people acting dumb," the vast majority of 4channers are actually quite stupid. 4chan users are generally obsessed to an unhealthy degree with anime, video games, and cats and almost always have a problem applying their unrealized genius intellect to any sort of work whatsoever. Their level of humor approaches that of a four-week-old child: an idea is funny because it is familiar. 4chan user hobbies include using IRC, watching lolicon ironically, and playing Pokemon. Because posting on 4chan is anonymous, any and all thoughts are posted. If the internet is a series of tubes, 4chan is the high-pressure, stuff-spewing junction of YTMND, GameFAQs, and every child enthusiast gathering in existence.
I've also actually met 4channers in one of my classes before, they used that little calling card phrase on me, "so I heard some things", but even before then I picked up on it pretty fast. They were very, very awkward people that used allot of inside internet jokes in everything, and thought they were quite intelligent and superior to everyone. They were pretty confused all the time too and easily irritable when they needed explanations. They came off as teenagers, not adults, it was kind of sad.
