What are role‑playing dice used for?

As the name suggests, these oddly shaped dice are used for tabletop role‑playing games. The most popular type of set is the polyhedral dice set, which contains seven different dice. Dice are usually referred to by the number of sides they have, so the familiar six‑sided die we know from Yahtzee is called a d6 (d for “dice”).
A standard polyhedral set includes a d4, d6, d8, d10, d100, d12, and d20.
 

There are also sets made exclusively of d10s (commonly used in various World of Darkness systems), as well as sets of only d6s or d8s created for specific systems or even specific classes within a system — for example, a “fireball set” made for a DnD wizard’s favourite spell.