A general purpose board mountable preset also called by others names like potentiometers, trimpots, etc but is basically just a variable resistor.
Trimmer/Trimpots is a high accuracy variable resistor and pcb mountable with 3 terminal pins. The voltage between the terminal varies as the trimpot is rotated. The Variable resistors are used for variating voltage as per the need in a circuit. The outer two pins are connected to Vcc and 0V, and cetner pin outputs a variable volatge between 0v and Vcc as the rotary cermet is rotated. The potentiometer is easy to mount on a PCB and can be adjusted using a screwdriver. This potentiometer has a single turn, which can be used to preset a value.
Note:- Picture is only for reference. Brand keeps on changing as per the availablity of the stock. Call for more info.