Activated ability

From Magic: The Gathering

Activated abilities are abilities of a card that their controller can use whenever he or she wants (providing that He/She can pay for it and barring special conditions (ie: Play this ability only during your turn etc...)). These abilities are always written in the form "{Cost}: {Effect}". Paying the cost allows a player to produce the effect. Costs may include paying mana, tapping the card, discarding cards, or other things. Like instants, these abilities can be played at nearly any time during the game (see timing and the stack). Activated Abilities, like instants, go on the stack.