Exponential rate is where the servo movement is not directly proportional to the amount of control stick movement on your transmitter. Over the first half on the stick travel, the servo moves less than the stick. This makes control response milder and smoothes out level flight and normal flight...
Both
Cheaper radio control systems are 1 to 1. How ever much you move a control results in an equal move in the model. More expensive ones can alter that so you can change how sensitive a control is at center and make it react more and faster the father you turn it.