Air assisted airless is a hybrid between airless and air spray. It uses the higher pressure of an airless system to atomise a coating that would be too heavy for an airspray gun, and compressed air to improve the atomisation, which gives a better finish.
An air assisted airless spray gun has 2 hose connections, one to feed the coating to the gun and the other to bring in the compressed air. Because you need a compressor to provide air for the gun, an air operated pump is often use to pump the paint to the gun.
Providing that the hose and gun are grounded (earthed) an air motor eliminates the risk of sparks from an electric motor.