In the context of the tabletop game that gives Dungeons & Dragons Online its name, a Warlock is a class defined by making a pact for power with some exceptional power. DDO simulates this by giving you laser beams that fire out of your hands. That’s admittedly glossing over the details (they’re actually more like orbs than laser beams), but if you want information on the class, you can just jump down to watch the class in action for an hour.
Yes, the most recent livestream from the game’s developers covered the Warlock extensively, focusing on what the class can do and how players can make the most of it. Best of all, you don’t have to make any dark pacts in order to see it in all of its pew-pewing glory; just hop on down and start watching the archived stream.