Second wind

Adventurers can dig into their resolve and endurance to find an extra burst of vitality. In game terms, an adventurer focuses momentarily on self-defense and spends a healing surge to regain lost hit points. Using one’s second wind is the one way that all adventurers have of healing themselves during an encounter. They must otherwise rely on other sources of healing.
    Unless otherwise noted in the stat block of a monster or DM-controlled character, this action is available only to adventurers.

Use Second Wind
         Action: Standard action. A character can take this action only once per encounter, so he or she can take it again after a short or an extended rest. A character can use his or her second wind without taking an action if another character administers first aid to him or her using the Heal skill.
         Spend a Healing Surge: The character spends a healing surge to regain hit points.
         +2 Bonus to All Defenses: The character gains a +2 bonus to all defenses until the start of his or her next turn. However, the character does not gain this bonus if he or she uses second wind as a result of someone administering first aid.

Published in Player's Handbook, page(s) 291, Rules Compendium, page(s) 248.