pre-
a prefix occurring originally in loanwords from Latin, where it meant “before” ( preclude; prevent ); applied freely as a prefix, with the meanings “prior to,” “in advance of,” “early,” “beforehand,” “before,” “in front of,” and with other figurative meanings...
amp
noun
1.
amplifier ( def. 2 ) .
an electronic component or circuit for amplifying power, current, or voltage.
lol - not trying to be an ass, that just comes naturally...
But seriously, it's the most accurate answer.
it's an amp that comes before anything else, like another amp or a mixing board.
The gain channel of a guitar amp (or a mixing board) is a preamp.