K-On! (けいおん! ,Keion!?) is a Japanese four-panel comic strip manga written and illustrated by Kakifly. The manga started serialization in Houbunsha's seinen manga magazine Manga Time Kirara since the May 2007 issue, and also started a bimonthly serialization in Houbunsha's magazine Manga Time Kirara Carat since the October 2008 issue. An anime adaptation produced by Kyoto Animation will begin airing in Japan on April 3, 2009. The title of the series comes from the Japanese word for light music, keiongaku (軽音楽 ?).

Source: Wikipedia