Dungeon Crawl is a turn-based game. Every action your character takes progresses the turn counter forward by one, and the game is paused between each of your actions. However, new players quickly observe that character and monster behavior can't simply be measured in turns.
Every character action has an associated delay, measured in aut (arbitrary units of time). Your delay determines how much time passes during a given turn for monsters to take their own actions. Monsters that do not act during a turn are still accumulating time for their next action.
The delay of an action is determined primarily by the type of action, but some are affected by other factors. Movement speed can be increased or reduced through beneficial or detrimental mutations (which some species begin the game with), or through wearing items of either running or ponderousness. Physical attack speeds are made slower by an amount dependent on your weapon's speed, but the speed brand and high skill in the associated weapon (or the Unarmed Combat skill) will reduce an attack's delay. There are also a variety of spells which can decrease or (rarely) increase the delay of several of your actions. As a result, well-equipped, high level characters can sometimes take multiple turns in the time it takes a monster to act once, but this depends on the particular monster you face. Although most are designed to act about as often as an average character, some can be significantly faster or slower than you.