Oh, didn't know you weren't sure of those terms--you should have stopped us before we went on and on!
I am oversimplifying to help you understand quickly:
Lows, mids, highs--refers to frequencies/pitch, not volume. So think of a choir: the bass singer has a "low" voice, and the soprano has a "high" voice.
Instruments can go lower and higher than our voices, so we usually talk about low/mid/high frequencies like this:
Lows--Drums (the kick drum), bass guitar
Mids--Voices, and most instruments
Highs--Drums (cymbals), string instruments (e.g. when a guitarist slides his hand across the strings)