What does it mean to 'activate' an ability in the context of the game?

Activating an ability in Magic: The Gathering refers to the process of using that ability, which involves putting it onto the stack and paying any associated costs to resolve it. This is a fundamental interaction in the game.

When a player activates an ability, they must adhere to the specific costs defined by that ability, which can include paying mana, sacrificing creatures, or fulfilling other requirements. Once the ability is activated, it goes onto the stack, allowing it to be responded to by other players before it resolves. This precise mechanism of activation is integral to maintaining the game's order and ensuring that abilities function as intended.

The other choices do not accurately define activation within the game's rules. Simply calling upon an ability without paying costs does not reflect the requirement to fulfill the costs, and using an ability only once per game or delegating it to another player are not consistent with the game's mechanics regarding ability activation.