These are small, metallic explosives that detonate from pressure. If your enemy runs over them, the mines will go off. They only last for a few moments, so be sure to drop them at the right time. A challenging weapon to use, but the damage it cause is worth all the trouble.
Twisted Metal introduced these as a weapon pick up, scattered around levels.
Twisted Metal 2 changed Drop Mines to a new list Energy Attack weapons that any vehicle could use. Four Weapons from Twisted Metal were changed, the others being the Freeze Missile, Rear Fire, and Jump (Catapult).