A general purpose board mountable preset also called by others names like potentiometers, trimpots, etc but is basically just a variable resistor.
It has 3 leads coming out of it. The outer two pins always have a resistance of 20K between them and the resistance between one of the outer pins and the center pin varies between 0 to 10K as the potentiometer is rotated.
This potentiometer can also be used as a variable resistor and to generate a variable voltage. To use this potentiometer as a variable resistor, connect the outer two pins to Vcc and 0 V and the center pin outputs a variable voltage between 0 V and Vcc as the potentiometer is rotated.