Manga is often mistaken for Anime, which is similar but different. Anime is short for Animation and is a sort of subset of Manga which relates more to film. Though certainly the two forms have influenced and fed off of each other.
Just as comic strips have many applications in Western culture, Manga has a variety of uses in Eastern culture and regularly touches on sports, romance, history, science fiction, the business world, horror and politics and can be found in just about any aspect of Japanese life.
In recent years Manga has become huge in America and online. In 2006, Wikipedia reports that the U.S. market for manga was taking in around $200 million. Whereas during the 70's Japan only had a small influence on American cartoons (Speed Racer, etc), now many of the mainstream cartoons show a direct influence (Dragon Ball Z, Pokemon, etc).
As Manga expands and becomes more and more popular and cross-cultural hundreds of new styles and subsets come into existence. You may have heard of Chibis, which are stylized Manga characters, or Q-version, a Chinese style where real life images are rendered in cartoon charictures. As the popularity of these styles increases the influences become more diluted and the boundaries between Eastern and Western animation and art styles will fade further and further.
