10 Sided Dice
The d10 is the only piece of the standard DND dice set that is not a platonic solid. The 10 sided dice we use in gaming is a pentagonal trapezohedron and is typically numbered 1-0, with the 0 representing ten. The d10 is a part of the traditional 7-dice set, but gained prominence with the launch of the World of Darkness games in the 90s, which used ten-sided dice exclusively for all rolls. Later the Legend of the Five Rings RPG also used only 10-sided dice.
The Origin of the d10
The oldest reference to a d10 that we have been able to track down is a 1906 US patent. Though the d10 is a part of the standard today, there was no d10 in the original Dungeons & Dragons dice set back in 1974. The d10 was first introduced to the gaming industry (with a claim of being freshly invented) at GenCon in 1980.
D&D and the d10
Today, d10s are used extensively in games like Dungeons & Dragons. Primarily, they are used to determine the damage of certain weapons and spells. A d10 can also be used in conjunction with another ten-sided die to make what is known as a percentile role. Percentile rolls allow players to roll within a range of 1 - 100.