Gunshot residue (GSR), also known as cartridge discharge residue (CDR), "gunfire residue" (GFR), or firearm discharge residue (FDR), is residue deposited on the hands and clothes of someone who discharges a firearm.

When a gun is fired small particles of firearm discharge residues (FDR) are produced from the bullet and cartridge case of the ammunition.  These residues escape through openings in the gun such as the muzzle and breech, and can be deposited onto the firer, as well as nearby surfaces.

If an individual handles a recently discharged gun or makes contact with an item or surface that has firearm discharge residues on it, this can also result in the transference of these discharge residues to that individual.

When a cartridge is discharged, small particles of Firearm Discharge Residue (FDR) are produced from the cartridge case components of the ammunition and these are primarily composed of both burnt and unburnt particles from both the explosive primer compound, and the propellant material.

FDR can be recovered from the hands, face, nostrils and hair of a suspect by; from their clothing; and from various surfaces, for example from within a vehicle used to transport the suspects, weapons and cartridges after a cartridge has been fired.

The analysis and interpretation of gunshot residues will help determine if a suspect may have fired a firearm or has been in the vicinity of a firearm when fired, or has been subject to contamination from sources of residue.