A 20K trimmer potentiometer, or trim pot, is a small adjustable resistor that is typically used to fine-tune the resistance in a circuit. The "20K" refers to its resistance value of 20,000 ohms. The "W203" refers to the specific package or housing type that the trimmer potentiometer is packaged in. It is commonly used in electronic circuits such as audio equipment and other precision instruments.

This small trimpot potentiometer is used to calibtrate circuits by adjusting the value of resistance in the circuit. Trimmer potentiometers require a screwdriver to change the value of resistance and are not indended to by adjusted often such as by the user of the device. Once you have set your resistance value then you will generally leave the trimmer potentiometer at that value indefinitely.