a. IR: Infrared, RF: Radio Frequency
b. Infrared is based on the "light" part of the electromagnetic spectrum; radio frequency is based on the "radio" section of the electromagnetic spectrum.
c. Basically, an IR remote control requires direct aim to the receiver in order for the signal to be received, but an RF remote control can be pointed in any direction to function if the signal is in the range.
d. Usually, RF costs more than IR.