Most people know that many an anime title has started as a manga (Japanese graphic novel). Yet not every anime fan is as familiar with the various categories of manga out there. Shoujo, manga for girls, and shounen, manga for guys, get a decent amount of attention as they each have publications dedicated to them (Shojo Beat and Shonen Jump respectively). However, there are many other genres out there. Namely the four panel comic (Yonkoma in Japanese).
Cultural Note: While we often categorize books and movies by type (Ex: Romance, Action, Science Fiction, etc), Japan’s categorization system is generally based on the intended audience.
The four panel comic relates to, well, comedy. Similar to our comic strips, four panels focus on giving a laugh or two. Many popular comedy-based anime have come from these four panel comics, including the ever popular Lucky Star and the now old, but still loved Azumanga Diaoh. Although most categories of manga have their own art standard, four panel art often varies from work to work. Some work that isn’t even official, such as the Melancholy of Haru-chan, becomes such a hit that it gets an official license and an anime production.
For a more extensive list on four panel comics, check out Wikipedia’s smashing Yonkoma list!