I'll second that. It's just an easy way of describing a sound. Alot of recording terms make more and more sense as you go on. Alot of terms are visual or tactile descriptions like dull, solid, brittle, warm etc. If you think about sound in terms of textures, shapes and feelings it all makes more sense. There's no set rule to how you describe something, you just say what you hear.
Words I'd probably use:
too much treble - tinny, harsh, skinny, too bright, brittle, too much top etc
not enough treble - dull, lifeless, flat, distant etc
nice treble - clean, clear, crisp etc
too much middle - boxy, whoompy (just made that one up), too middley etc
not enough middle - scooped, hollow etc
nice middle - warm, full bodied etc
not enough bass - skinny, weak, flat, limp, too bassy etc
too much bass - too heavy, farting, boomy etc
nice bass - tight, fat, rounded, pumping etc
I'd use the word "boxy" if I'd put a mic on a snare or kick drum and not gotten rid of those nasty middle frequencies and there was no definition in the treble or bass frequencies.
Play a CD through an EQ and and change the frequency you boost or cut and see what it does to the sound in terms of making it bright, flat, boxy, boomy etc. You learn loads that way.
