Electrical Gurus: Potentiometer vs VR?

The three legs are;
Source = power supply
Wiper = the resistive counter
Ground (not neutral) = just as it says

Normally used in a circuit where "gain" is required to fine tune a "null" or movement, whether power or resistance.

Rheostats are typically used more for current control like a dimmer circuit. The rheostat is a single variable resistor where the wiper sweeps across the resistor to vary the current through the circuit. The wiper is connected to one of the legs.

A pot is more of a variable voltage divider circuit. Kind of like having two resistors with the wiper being in the middle and varying the resistance ratio of the two resistors. The wiper stands on its own and is used to pick off a voltage at a specific point in the circuit.