The NEC refers to many cable ratings that specify where a cable should be installed. A plenum cable is one that is put in the air ducts at the top of the ceiling. Plenum cables are fire-resistant and emit less smoke than typical cables, making them safer in the event of a fire.
Non-plenum cables, unlike plenum cables, cannot be put in air ducts or plenum regions. Non-plenum wires must instead be put within walls and across open ceilings where air is stagnant. Non-plenum rated cables have a chlorine-containing PVC or polyvinyl chloride jacket. As PVC burns, hazardous chemicals are released into the air, posing a health concern. This type of cable is typically used with speaker wires and audio cables.
A riser cable is designed for vertical runs or runs along floors. This cable is also known for being fire-resistant and unlikely to provide a safety concern during a fire.