1D20 (or simply D20) refers to a twenty-sided dice, which is composed of triangles. In geometry the shape of its body is called Ikosaeder.
Dice are used in pen & paper roleplaying games, and also in their computer equivalents, to introduce a factor of chance.
In The Dark Eye and in Drakensang as well, this dice is used for Attribute and Talent Tests. In case of Talent Tests, this dice is rolled three times.