Often found in old-school arcade shooters such as Unreal Tournament, multifunction ammo can behave in more than one way when fired from the same weapon. It can even be employed by itself as an entirely different weapon; for example, the player can use ten bullets to make a grenade in Soldier of Fortune.
The image on the left is an example of multifunction ammo, the rocket launcher can use its own rockets to fire grenades, notice, the rocket have wings deployed and the engine ignited and the grenade have no wing deployed and the engine is off (the rocket will explode on impact, and the grenade will bounce and explode after a few seconds) In Quake there is the same thing however, rockets deserves to act like rockets in the rocket launcher and grenades in the grenade launcher. The concept was pushed further in the game Gunman Chronicles, where rockets could work like grenades, laser triggered mines, or missiles, and could contain different payload types.
This concept doesn't include energy-based weapons, which are flexible by nature, and weapons that can use anything in the world like the Half-Life 2's Gravity Gun