A prop gun is not always a toy or fake gun and it can be, in fact, a fully functional weapon.
According to the website of The Specialists LTD, a company that provides prop weapons to Hollywood productions, prop firearms fall into three categories.
Blank-firing guns are real guns that fire blanks - bullet shell casings with no projectile.
Replica guns are made with metal, resin, plastic, or rubber and designed to look identical to real guns. They do not fire.
Non-guns are similar to replica guns but have the added feature of an electronically triggered muzzle flash - the light created by a blast - to simulate a weapon firing.
A spokesperson for Baldwin said in a statement that the incident involved the misfiring of a prop gun with blanks.
Television writer David Slack, who has credits on series such as Law & Order (1990 to present), tweeted after the tragedy: "Prop guns are guns. Blanks have real gunpowder in them. They can injure or kill - and they have."