Manga is the name given to the japanese comics, which are characterized by being read from right to left, unlike conventional Western comics.
Its origin is in the Theater of Shadows, which in feudal times roamed several villages telling legends through puppets. These legends ended up being written on scrolls and illustrated, giving rise to stories in sequence, and consequently giving rise to manga.
Several manga give rise to anime, which are shown on television, in video or cinemas, but there is also the reverse process, when anime becomes a print edition of a story in sequence or of illustrations.
The current form of manga emerged in the early 20th century, under the influence of Western trade magazines and newspapers, coming from the United States and Europe, which brought humor, social and political satires in short strips of one or four frames.
The manga cover all topics such as school life, work, sports, love, war, fear, Japanese and Chinese literature, economics, finance, and much more.
Manga are generally classified according to their target audience. The stories that are made for boys are called shounen, like One Piece, Naruto and Bleach, for example. On the other hand, stories aimed at entertaining girls are called shoujo.
There are also other genres, such as the gekiga, which is more aimed at an adult audience, not necessarily with adult themes such as pornography.
See also: the meaning of fanfic, shippar and fandom.