Teamwork and Roles

MOBAs like WoW PvP, are a team sport. (Whether the players actually act like a team is another story, of course.) Dota 2 has built in voice-chat, to facilitate team communication. Unlike WoW PvP, every hero in a Dota match is filling one or more roles. Think of a high level heroic boss fight in WoW. Every player has a role - tank, healer, crowd-control, DPS. Likewise, in MOBAs, every hero on a team has one or more roles. In Dota 2, you have Supports, Carries, Nukers, Gankers, Disablers, and Initiators, as well as various other roles. This wiki article on the dota2wiki covers the roles in detail, and very well.