Terminal velocity is the point at which, during freefall, the surface area of the downward-facing side of an object collides with enough air particles to balance out gravity so that a constant speed is reached. A favourite GCSE question uses a parachutist as an example - when the chute opens, the surface area increases, so terminal velocity would be a lot slower.
Another example of this would be if in a vertical race, one skydiver jumped in a "dive" position so he would be vertical, and another jumped in more of a "belly-flop" position. The dive position would move faster since there is less resistance.
On the Moon, however, there is not enough atmosphere to make any difference - on one of the later Apollo missions one of the astronauts dropped a feather and a hammer at the same time from the same height. They hit the ground at the same time since weight is immateriel to gravity, and there was no air resistance to slow the feather down.
So while gravity is only one sixth that of Earth on the Moon, if the objecty had enough time, it would probably reach speeds close to the speed of light before the air resistance can cancel out acceleration.