What is the difference between air resistance and drag??

It is a force similar to frictional force which is offered due to air on moving bodies. It slows down the moving bodies by providing an opposing force to the motion. It depends on the relative speed of the moving bodies.

Air drag

 

Air drag basically means the resistance offered by air to the flow of any body through it. So, air tends to slow down any body travelling through it.

For example. when we throw a ball horizontally it gradually slows down and falls to the ground due to air resistance. 

Similarly, like air, all mediums exert resistive forces to any body flowing through them.