What does the following image represent?

The figure given represents a Rheostat. A Fixed Resistor is a resistor having a fixed or defined resistance. A variable resistor is a resistor which is used to control the current by varying the resistance. There are two types of variable resistor: rheostat and potentiometer. A rheostat has two usually two terminals (one fixed and the other moveable) while a potentiometer has three terminals (two fixed and one moveable).