Distance Protection is for Transmission Lines and works on the principle of calculating the impedance up to the point of fault. It needs both Voltage Input & Current Input.

Differential Protection operates on the principle of calculating the difference between two currents inputted to the relay. It is used for machines like Transformers, Generators, Motors and also for Bus bars in sub-stations. You need to give two current inputs to the relay.

I agree, you can also use differential protection to protect short overhead lines and it is usually the main type of cable feeder protection using relays such as solkor and translay in conjunction with pilot wires. The rule of the thumb in differential protection is 'what goes in must equal what comes out'

spelling...joke.. the difference is that the way how these relays work or the principles they are using. 1st, the distance relay, it calculates the impedance of the protected equipment, if the calculate impedance is less than the impedance of the protected equipment (typically 80%) it will then issue a tripping signal - which means there is a fault. 2nd, Differential relays, are unit protection, it compared the in and out of certain quantities that flow across the protected equipment, most likely, it compares the in - out of currents. I hope it is clear.