What's Digimon?Digimon is short for Digimon: Digital Monsters. Digimon is a TV show, several movies, lots of games, other merchandise and the subject of more websites than you can imagine!
Digimon TV show currently has 4 seasons (released). The seasons
Season 1: Digimon Adventure
Season 2: Digimon 02
Season 3: Digimon Tamers
Season 4: Frontier Kids
There are 8 Digimon movies made in Japanese. These are quite short, so 3 of them have been combined to form Digimon: The Movie, the only Digimon movie that has been released in English so far.There are Digimon video games for the PS/2 and GBA platforms. They have been translated into English too :).
There's also a Digimon Battle Card Game, where you build a deck of trading cards and battle other people, much like the Pokémon TCG, and Digimon trading cards.You can also get Digimon Tamagotchis, electronic Digivices and other non-electronic games and toys.
As for websites, you'll find the official site at http://www.digimon.com/ but there are literally thousands of fan sites that have sprung up on the Net, such as this one.