A sling is a projectile weapon

Weapon

A weapon, arm, or armament is a tool or instrument used with the aim of causing damage or harm to living beings or artificial structures or systems...

 typically used to throw a blunt projectile

Projectile

A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....

 such as a stone or lead "sling-bullet". It is also known as the shepherd's sling.

A sling has a small cradle or pouch in the middle of two lengths of cord. The sling stone is placed in the pouch. The index finger is placed through the loop, the other string has a tab that is placed between the thumb and forefinger.