Difference between rheostat and potentiometer 

Rheostat

Two terminal devices: The rheostat is a two-terminal device that only forms a connection to one end and a wiper or slider.
Main purpose: The main purpose of rheostat is to vary the amount of current.
Instrument type: it is considered as a variable resistor.
Composition: The rheostat is composed of different materials like a metallic ribbon or carbon disks.
Connection type: It forms a series connection with the circuit.
Suitability of use: It is suitable for high power application.
Application: In device testing purposes, rheostats are used in the laboratory. They are also used for controlling the motor speed. Apart from this, their main use is to control the intensity of the light by connecting it in series with the light. When increasing the resistance, the luminosity of the light decreases while the luminosity is increased if we decrease the resistance.

Potentiometer

Three terminal devices: A potentiometer is an instrument of three terminals whose ends together with the wiper are attached to the circuit.
Main purpose: The potentiometer configuration is used to feed voltage in any circuit.
Instrument type: It is considered a type of sensor.
Composition: The composition of a potentiometer is the graphite material.
Connection type: It is mostly connected in parallel connection with the circuit.
Symbol: 
Suitability of use: The potentiometer uses are mainly in low power application.
Application: They are mostly used in electronics circuits to vary input voltage and can be used as a displacement transducer. The common and well-known application of potentiometer is audio control as they are used in an audio device to control the loudness.