The second wind action is a standard action that allows a character to spend a healing surge to regain hit points and gain a +2 bonus to all defenses until the start of the character's next turn.
A character can use the second wind action only once per encounter. Like an encounter power, second wind is renewed after a short rest or extended rest. There are also powers that allow a character or ally to spend healing surges without using second wind.
Only player characters can use the second wind action, unless the action is specified as one of an NPC's or monster's abilities.