In electronics, a potentiometer or pot is a jargon term for any kind of variable resistor. Control of the pot may be exposed to the user via some kind of knob or slider, such as a volume control, or can be hidden as a preset control, adjustable with access to the circuit board using a screwdriver. Physically, a pot consists of a conducting shaft and armature. The end of the armature is a contact point, which moves along a track, usually made of carbon or some other conductive material. The shaft is one terminal, and the two ends of the track are the others.
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The simplest pots are linear. The ratio of the resistances corresponds to the proportion of the distance along the track. Volume controls are different. As the human brain perceives volume on a log scale (decibels), volume controls are constructed to give a logarithmic relationship between the resistances, and the distance moved along the track.
Stereo hi-fi systems have double gang pots. A single shaft has two electrically isolated sections, moving pointers along separate, disconnected tracks. One track is used for the left channel and the other for the right channel.
In consumer electronics, pots have in the main, been replaced by digital circuitry, which has the advantage of having no moving parts to go wrong (apart from the up and down buttons of course).
A derogatory term among television engineers is "pot twiddler" - someone who can fix minor problems such as picture quality, by twiddling pots, but hasn't a clue how to diagnose, let alone fix anything more major.