Phono input is a set of input jacks, usually mini jacks or RCA connectors, located on the rear panel of a preamp, mixer or amplifier, especially on early radio sets, to which a phonograph or turntable is attached.
[1] Modern phono cartridges give a very low level output signal of the order of a few millivolts which the circuitry amplifies and equalizes.
This is accomplished in the amplifier with a phono input that incorporates standardized RIAA equalization circuitry.
By the 2000s only very sophisticated and expensive stereo receivers retained the phono input, since most users were expected to use digital music formats such as CD or satellite radio.
This "phono input" designed for the millivolt signal from an unamplified turntable should not be confused with the modern standard one-volt line input and output that also uses RCA connectors and is found on video cameras, recorders and similar modern equipment.