Here are some images of types of Potentiometers or variable resistors. Pots or Potentiometers have a Shaft on which a knob can be fixed. These are used on Instrument panels to vary or control parameters like voltage, current, temperature etc. It is like a GUI element for Electrical and Electronic Systems. It is a basic Human Machine Interface and as old as Valve Radios. The Huge Rheostats are its ancestors but these giant pots are used in Large Electrical Circuits.
In Electronic Circuits Rotary Pots and Sliding Pots are the defaults. These days they have been replaced by digital controls and even touch interfaces.
In Instrumentation the Multi-Turn Wire Wound Precision, Linear Pots from Bourns or Spectrol are still used where a fine analog control is needed. Some Industrial Joysticks have also applied these.
The Single Turn Carbon Film Rotary and Sliding Pots are used today too for Volume control and Light dimming boxes. It was used in Analog TVs and Audio Systems for decades.
The Wire wound Instrument pots have good Temperature Stability and higher wattage and many operations. These make it useful in Industrial Process control. Some of the applications are in Timers and Motor Control. It is also used to set analog parameters in a control system.
Multi-Turn Trimpots and Single turn Presets are mounted on the PCB for Calibration or Adjustments of circuits. This is done using a Plastic Screwdriver called Tweaker. Some presets are dust proof. You have both the stable Metal Film and affordable Carbon Film. Vertical and Horizontal Mount.