Exalted is a triggered ability in Magic: The Gathering. The rule states that whenever a creature attacks alone, the creature with exalted gets +1/+1 until the end of the turn.
A creature is defined as attacking alone if it is the only creature declared as an attacker during a given phase. If multiple creatures are attacking and all but one are removed, the exalted ability does not trigger. Also, it does not have to be the creature with exalted attacking. Any creature can trigger the ability. The ability lasts until the end of the turn. If there are special circumstances that add additional combat phases, the creature retains the ability. If one creature attacks again, the exalted ability triggers again.