What is the difference between air resistance and terminal velocity?
Air resistance is the force that the air applies on the body which decelerates the body. Terminal velocity is the velocity (speed in a given direction) at which the air resistance will be equal to the weight of the body. For example, when the rain drops reach the terminal velocity the weight of rain drop is matched by the air resistance. Hence the rain drop will not accelerate and continues to fall down at the constant terminal velocity (remains constant if the air resistance remains constant).