From Wikipedia:
Potentiometers (often abbreviated as "pots") can be used to control a variety of functions inside an electric guitar. Most often they function as tone and volume controls, but can also blend two pickups together, attenuate one coil of a humbucker, and so on.
Potentiometers are differentiated by their electrical characteristics, of which the following are most important in an electric guitar:
Value – the resistance between the two outer lugs. The most common values are 250 kΩ (for single-coil pickups) and 300–500 kΩ (for humbuckers), although values ranging from 50 kΩ to as high as 1 MΩ have been used. 25 kΩ pots are usually used with active electronics.
Taper – the ratio of wiper travel to the resistance between the wiper and the outer lugs. Logarithmic pots (also known as "log" or "audio" pots, and designated with the letter A) are generally used for volume controls, due to the human ear's response to sound pressure being roughly logarithmic, whereas tone controls can employ both logarithmic and linear pots (designated with the letter B), depending on personal preferences and wiring arrangements. Reverse audio pots are sometimes used for volume controls on left-hand guitars, but this is not widespread due to the relative rarity of such pots.
Besides the common pots used for volume and tone controls, a number of specialised types exist:
Push-pull pots – these pots incorporate an on-on DPDT switch on the underside of the pot that's actuated by pulling the shaft outwards and pushing it back in (hence the name). The switch is electrically independent from the pot and can be used for a number of functions.
Push-push pots – a variation of the above, these pots also incorporate a switch which is activated and deactivated by pushing on the middle of the knob. This is used by Fender in their S-1 Switching System, and unlike push-pull pots, requires a special knob.
No-load pots – also used by Fender, these pots have the clockwise lug disconnected from the resistive strip within, resulting in infinite resistance between the wiper and the other outer lug when turned fully clockwise. These are sometimes used as tone controls, to remove the load on the pickup(s) presented by the pot and the tone capacitor when turned to 10.
Dual-gang pots – these are simply two pots stacked together, either with concentric shafts, allowing the independent control of two different parameters, or with a common shaft. The latter type can be used for blending the signals of two pickups together, and they usually feature a detent in the centre position.
Check out this video of a person reducing the crackle that can sometimes occur within pots.
Thanks to Wikipedia!
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