Flashbang grenade

The Flash-Bang Grenade or Stun grenade

is a special type of grenade used by the UNSC. Unlike Fragmentation Grenades, these grenades are not necessarily lethal, they pack exposive force and shrapnel, but they are more designed to stun a target instead of killing it immediately. 

There are a variety of uses for these, they have been used in military exercises by the UNSC, at least since 2525. They are also occasionally used in combat as well, serving to confuse, disorient, or momentarily distract a potential threat for up to five seconds. A flashbang can seriously degrade the combat effectiveness of affected personnel for up to a minute.