Manga are Japanese comic books. Manga is often made into Japanese cartoons, or Anime. The art in Manga has a very definite look to it and is often referred to as Manga Style.
(Maw Nnnnn Gah) In Japanese, it is actually three syllables, although the middle "N" is spoken very quick. Americans have a habit of pronouncing it "Man-Gah", but that is not actually correct.
The word Manga can be translated as, humorous pictures. Manga became very popular in the 20th century when laws prohibiting the publication of those kinds of items were lifted. It has since become a huge part of Japanese culture. Unlike in America, Manga is read by most people in the country. The artists and writer of Manga are well respected for their work, much like the writers of literature in America.
Recently, Manga has become popular in America. It has been a very successful new medium that has become very popular with young people. Manga, and the Anime that it has inspired, has been seen on T.V., in movies, and has even influenced the art styles of certain American artists like Ed McGuinness, Brian Wood, and Frank Miller.
In Japan, a lot of Anime is based on popular Manga, but in America, it is usually the other way around. Most of the times, publishers will wait until an Anime has been released through stations like Fox, Cartoon Network, and The WB. Then the Manga will be published in conjunction with the release of the cartoon.