Servo: the motor/gear drive unit in the R/C control system which is used to move the control surfaces (moves levers, pulls and pushes wires) Has circuitry to compare actual position with desired position, as given by the reciever.

ESC: (Electronic speed control) an electronic varial resistance/variable voltage device used to control electric motor sped, primarilly used in electric powered models.

ESV: (Expanded Scale Voltmeter) A device for measuring the voltage remaining in a battery pack.

RX: (Reciever) The radio control system's sensing device that interprets the radio transmitter's signals, converts them to a form useful to the servos for determining the desired control positions.

(there's a few... )

Visit my site. Read the beginner's guide. Then follow the link I have to "Best info for beginners ANYWHERE!" (Mr Sullivan's page, which gets into deeper detail)
http://www.geocities.com/fredhh/FHH_Homepage.html