Quote by BeaverHunter:
What the hell is a moba? Is it multi-player hack n slash button mash? I do not comprehend.
Moda stands for Massive Online Battle Arena. Basically 2 teams (usually 4v4 to 6v6) will compete against a common objective using a combination of melee, ranged and magic attacks. Most will have checkpoints and other areas you fight over to edge the battle across a map.
The most common two examples are definatly Defence of the Ancients and League of Legends (both of which are free by the way if you want to try them out).
In my opinion these games have viscious learning curves and when not playing with skilled players can be long and monotonous but I've heard once you get a good team together they can be a hell of a lot of fun.