A drop gun is an illicit backup weapon carried by someone, typically a police officer, who has a primary weapon in their possession. The term "drop gun" is also used to describe an unregistered firearm carried by policemen to "drop" at the scene where a pursued suspect has been shot. This is done to justify shooting or killing a possibly unarmed suspect. The use of drop guns is illegal and unethical, and it is not a common practice among law enforcement officers.

In the context of the Natural Selection game, "drop weapons" refer to the ability of the Marine Commander to drop weapons and equipment in a radius around the structure.

It is important to note that the use of the term "throw-down gun" is also used to describe a firearm planted by police officers to justify a shooting. This practice is also illegal and unethical.