What is a multi-purpose ABC fire extinguisher?

A multi purpose ABC fire extinguisher has the ability to extinguish class A,B, & C class fires by effectively smothering them, which in turn separates the oxygen and fuel. They are the all around work horses of the fire extinguishing community. The key ingredient to these types of extinguishers is ammonium phosphate. It is a non-conductive, corrosive agent that does a good job of suppressing fire at the cost of making a complete mess.