A guy I've been recording with for years has a single word that wears many hats: "flat." Off-pitch? Flat. Dull, woolly tone? Flat. Treble-y and missing body? Flat. Phase-y? Flat. Overcompressed? Flat.

One word I've had a lot of success with when dealing with the artist is "undefined." As in, "That kick drum is sort of undefined." It's not too specific, but it gets the dialogue going, and then some experimentation with level, EQ, filter, compression, etc, in an effort to find some "definition" for the track that works in the context of the mix. I think it works well because the artist can often suffer from the "Ooh, that's me coming out of the speakers!" syndrome: they're excited to hear their own music coming back through (hopefully nice) monitors, and aren't really sure what it should sound like in the context of both the mix, and the vision they hold in their own mind for their music.

My first language is Italian.

I find that very descriptive hand gestures work well when defining these ;)

I think you are being too kind to the talent there; "Turn it up" should really be "Turn ME up"!

As Tech support in High End Audio, I get this sort of question all the time, here’s my take on the question:
The vast panoply of verbose, subjective adjectives that Audio-geeks use to describe various sonic artifacts are beyond in-exact, but in general do have (theoretically) functional meanings.
Harmonics:
Let’s go with the scientific definition here. When you view a pure tone from a signal generator(on an oscilloscope, you see a graph with a single spike at the frequency you are generating, this is the fundamental. When you play that ‘A’ on a guitar, you will see that same spike, but to right and left of it on the scope, you will see smaller spikes at intervals above and below the frequency of the fundamental, this is the harmonic content that makes up the character of the note. That ‘A’ note played on a piano will have harmonics at different intervals and amplitudes, which is how you hear the difference between a piano and a guitar. A processor that is said to add harmonics is really boosting frequencies where the harmonics the processor designer has targeted lie, like a BBE sonic Maximizer.
Roundness:
This typically comes from boosting odd-order harmonics (as tubes tend to do) and/or introducing Bell-Curve distortion. Solid state gear in general produces clipping distortion, seen on the O-scope, the top of the wave is actually clipped off, this will produce a harsh sound, but just a little of it will produce ‘punch’ as well. Tubes produce Bell-Curve distortion, instead of clipping the waveform, it kind of squishes it, making it shorter and fatter, but keeping the general shape of the wave, this results in ‘warmth’ or roundness, imparting nice smooth sound to mid range in the female vocal, violin and saxophone area.
Presence:
This is typically an upper mid / lower highs EQ boost and a touch more even-order harmonics.

Punch:
I believe a lack of ‘Punch’ typically comes from woofer ‘hangover’, as the woofer moves back and forth to reproduce the sound, the amplifier needs sufficient output current to completely cancel the inertia of the moving cone, stop it on a dime and move it back in the other direction, if it fails to do so, the woofer will have hangover, and lack definition and punch. A fast slew rate and rise time in an electrical circuit will also increase punch.
I am unsure if ridged, definitive terms can ever be created for such things and personal opinion will be the norm here, people in audio constantly make up their own definitions, miss use terms and totally miss interpret in-complete information, making up explanations to suite their purpose of the moment. I am very likely guilty of this in the above missive as well, so I will leave you with this thought:
“How do you tell the difference between a used car salesman and an audio salesman?”
“The used car salesman KNOWS when he’s lying!”
Chuck Hinton
McIntosh Laboratories Technical Services
Sometime contributor to Home Toys and FolkWax magazines

Love this post! Laughing for real.

I do think increasing harmonic distortion in general makes people smile. Some pres have a nice harmonic dist range. All those adjectives are, IMHO, just people trying to describe this really subtle, but nice, quality they hear happening on different sources. And I agree - its total mumbojumbo.

I think "that sounds GOOD" is way more accurate.

Words and meaning are often lost when people communicate.
Take simple communication between people of different gender but normal persuasion. For instance, two young good looking people meet in a bar and start talking... The words are careful and polite, neat and happy selling friendship and kindness, well, if you're doing your job right... Now, let's change some things, the people in the bar are now a young male and an old male, looks are irrelevant... Humor is now the only goal, words become blunter and more pointed at the same time whilst expression and delivery are louder and more gregarious than before, without the prospects of fucking and only either a laugh or a fight on the table the conversation is always different...

What does all this mean?

Well, how well do you listen?