Electronic component forming a three-terminal resistor with a sliding contact. Acts as a variable resistor / voltage divider, manipulating the amount of current flowing through it.
Potentiometer - short form pot. Electronic component forming a three-terminal resistor with a sliding contact that acts as a variable resistor / voltage divider and lets a variable current flow through.
Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment.
Potentiometer Explanation: http://www.electronics-tutorials.ws/io/io_2.html
Voltage Divider Tutorial: https://learn.sparkfun.com/tutorials/voltage-dividers