Polyhedral dice

In a wide variety of role playing games, a number of polyhedral dice are used.

Typically, these dice are referred to by the number of faces they have: a 'd6' is a regular cubic die, pronounced 'dee-six'.

d4	tetrahedron	Each face has three numbers: they are arranged such that the top number is the same on all three visible faces.
d6	cube	A common die. Opposite faces must add to seven.
d8	octahedron
d10		Each face is kite-shaped; the smallest angle of five faces point to one edge, the smallest angle of the other points to the opposite. Not a regular polyhedron.
d12	dodecahedron
d20	icosahedron
d100 d%		Usually modelled by rolling two d10, one labelled 00,10,20..90, the other normal. Examples do exist of 'true' d100's, but these are rare, and given the nickname death stars due to a passing resemblance to the Star Wars ship.

Often the names of the dice appear in formulas for calculating game parameters: eg, hit points. '6d8+10', for example, will yield a number between 16 and 58 with a bell curve distribution, as it means 'Roll an eight-sided die six times and add ten to the total of all the rolls'. Occasionally they may be written '10×d6+20'; this means 'roll one six-sided die. Multiply it by ten and add twenty', and avoids boring repetitive dice-rolling.