A style of roleplaying
with a closer resemblance to storytelling
or improv theatre
than to the better-known dice-using style of roleplaying games
In games with dice, the outcome of tasks is usually determined by setting a difficulty for a certain task, and the performer of the task must hope to roll higher than that difficulty, or else fail the task. Conversely, in diceless games, the gamemaster compares the skill level of the character with his own preset difficulty for the task and internal knowledge, and decides for himself whether the character should have been able to make it.
Proponents tend to favor diceless for its speedy resolution of events and more attention to story; opponents feel it places too much emphasis on the gamemaster's judgment and too much power in his hands. (It is worth noting, however, that if one does not trust one's GM, one should probably not be playing in his game in the first place, dice or no.)
Notable diceless RPGs include Erick Wujcik's Amber RPG, and R. Sean Borgstrom's Nobilis.