I’m no expert in electronics, but I do toy around a little as a hobby. I’m familiar with the use of rheostats to vary resistance, but don’t really understand the reason for the third pin on a pot. What kind of applications are all 3 pins used for, and what function does it serve?
Dixon
A potentiometer is named for it's property of producing a variable voltage, ie electrical potential. A voltage is applied across the full resistance and the variable potential is between the moveable terminal and one end.
Philomel
Read this tutorial:
https://www.circuitstoday.com/difference-between-potentiometer-and-rheostat
billrussell42
the three terminals act as a voltage divider. see drawing. The pot replaces the two resistors on the left but allows continuous adjustment.
for two resistors
Vout = Vin(R2) / (R1+R2)
for pot with k being percent rotation from 0 to 100%
Vout = kVin/100
used, for example, as level controls in audio.