Is battle.net the official server of Warcraft

Battlenet is the official online component of Blizzard Entertainment for World of Warcraft, Warcraft II: Battlenet edition and Warcraft III, Diablo and Diablo 2, Starcraft and Starcraft 2. It allows chat and cross-game friends list.

Note: Battlenet is required for most of the newer online Blizzard games like World of Warcraft (not new, but required) and Starcraft 2.