A Frag Grenade.
A frag is any small bomb that can be thrown by hand. Hand grenades are classified into two categories, explosive grenades and chemical and gas grenades. Explosive grenades are the most commonly used in modern warfare, and are designed to detonate after impact or after a set amount of time. Chemical and gas grenades are designed not to explode, but to burn or release a gas.
Grenadiers were originally soldiers who specialized in throwing grenades.