Have you checked Wikipedia?
We really shouldn't belittle or discourage people from asking questions...that's the purpose of a forum. If you don't like it or for some reason think it's not worth your time...move on! It's these type of responses that kill open discussion.
Kind of passive/aggresive of you to include the link to underscore you distain...nice touch.
Jwilsco, I'll try and explain...let's see how many people make fun of my explanation.
The term phono, short for phonograph is your turntable input.
A preamp inputs and outputs "line level" signals such as a CD player, DVD, tape deck. These components have a specified gain in audio signal that can be accepted and processed by the preamp.
The cartridge on a turntable outputs a much lower level of voltage compared to a line level. It needs to be amplified to a high enough level to get into the preamp.
A phono preamp boosts the voltage level from the TT. More commonly called a phonostage, the TT (or phono) will now closely equal a line level and can be plugged into the preamp.
A second very important function of the phonostage is to take the raw recording off the vinyl record and equalize it. Vinyl is cut using RIAA Equalization which boosts the high frequencies and lowers the bass frequencies allowing more room for grooves to be cut.
After the phonostage has EQ'd these frequencies, out comes music.