grenade

A grenade is a type of explosive device that's small enough for one person to carry.

Imagine you're watching a movie with lots of action scenes - you might see someone throw a grenade at the bad guys. In real life, grenades are used by soldiers and military forces as a way to attack an enemy from close range. They can be thrown or attached to things like a wall or a door to cause damage when they explode. If someone says "the police threw a stun grenade" it means they used one that's designed to distract or disorient, but not necessarily harm people.