The dice pool is a mechanic in table top RPGs that employs collections of dice as the main mechanic in task resolution. The granddaddy of all table tops, Dungeons and Dragons, used individual die rolls (most notably the d20) to decide outcomes. Numbers would be added directly to the roll and it would either reach the target number or not. This was the basic formula for decades and it works fairly well but has a downside. It requires addition or subtraction with every roll which can become unwieldy with higher numbers and bog down the game. It also provides a flat range of probability rather than a bell curve which is arguably unrealistic.
One solution proposed to this is dice pools. Instead of adding to a roll; set a target number and roll multiple dice then either add them together or count the number of dice that met or exceeded the target. The exact way this works varies by game. White Wolf's Storyteller System sets target numbers for d10s then has the degree of success determined by the number of successful rolls with one succeeding roll being the most marginal of wins and more counting toward ever greater levels. Fantasy Flight's Legend of the Five Rings RPG require a certain number of successes rolled and limits the number of dice that can be kept from among a group. Dead Lands employs multiple dice sizes as well as dice pool creating a huge range of possible rolls. Most dice pools have players reroll or explode when a die come up with its top value which gives an extremely small but real chance of hitting any number. Dice pools are probably the second most common task resolution mechanic after single modified die. Their only real downside is that they tend to lack granularity meaning that power increases in leaps and bounds.
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