Saintsman,
A propeller is device that produces thrust to propel an aircraft forward and is designed for a particular forward speed.
A rotor is a propeller optimized to produce static thrust.
Other than that, the two are very similar.
Any propeller can be used to produce static thrust, but the larger rotor is more efficient for static thrust or lift (thrust is the same as lift, we often use either word when talking about rotors).
The early helicopters had large rotors and heavy engines. As engines get lighter, rotors get smaller. Eventually rotors will look like propellers.