Magic represent a supernatural power that dwells inside a world and can be handled in different ways by characters with specific skills.
In roguelikes, magic represent a group of skills that almost always consumpts finite or regenerative resources from a character in order to produce an offensive, defensive or supportive effect uppon the character, another characters or the game world.
It is common for each roguelike to have its own Magic System, representing the agrupations of different magical effects as well as defining the rules for the use of magic.
Magic is the main alternative to the common Hack'n Slash strategy in roguelikes, allowing the player to refine his attack choices according to the situation, thus making wizards more powerful than warrior, if the character has advanced enough and the player knows how to play the game.
Wizard are commonly weak at the beginning, but grow more powerful than warrior classes in the long run.