Recharge

Some special abilities have restrictions on the number of times they can be used, but can recharge when depleted:
Recharge X–Y. The notation "Recharge X–Y" means a creature can use a special ability once and that the ability then has a random chance of recharging during each subsequent round of combat. At the start of each of the creature's turns, roll a 1d6 . If the roll is one of the numbers in the recharge notation, the creature regains the use of the special ability. The ability also recharges when the monster finishes a short rest or long rest. For example, "Recharge 5–6" means a creature can use the special ability once. Then, at the start of the monster's turn, it regains the use of that ability if it rolls a 5 or 6 on a 1d6 .
Recharge after a Short or Long Rest. This notation means that a creature can use a special ability once and then must finish a short rest or long rest to use it again.