Spell level is a number between 0 and 9 that defines the spell's relative power. Level 0 spells are also called cantrips, and epic spells are sometimes called level 10 spells. The most direct consequence of spell level is its effect on the DC of saving throws; spell level is one of the addends in the formula. In addition, it is possible to have immunity to spells below a certain level (c.f. globe of invulnerability).
In spell descriptions, the level is preceded by an abbreviation for the class whose members can cast the spell. The level entry also indicates whether a spell is a domain spell and, if so, what its domain and its level as a domain spell are.