What does it mean to play an ability according to the current rules?

Playing an ability refers specifically to the action of activating an activated ability in the game. This involves choosing to use the ability, following the necessary steps as outlined in the rules, which typically include paying any costs associated with the ability, such as tapping a permanent or paying mana, and observing any timing restrictions.

Activated abilities often come in the form of a cost followed by a result, for example, "Tap: Draw a card." When a player activates such an ability, they are effectively "playing" that ability. This term is crucial because it isolates the concept of utilizing an activated ability as an action distinct from other game actions, such as tapping a permanent for mana, revealing cards, or sacrificing permanents.

The other choices, while relevant actions or concepts within the game, do not fall under the definition of "playing an ability." Tapping a permanent for mana is a part of the game mechanics but does not encompass all aspects of abilities. Revealing a card has no direct relation to playing an ability, and sacrificing a permanent is typically a cost associated with some abilities but not the same as activating them. Therefore, the definition of playing an ability is correctly captured by the activation of activated abilities.