Terms describing how the sound feels.

Aggressive
Forward and bright sonic character.
Airy
Spacious. Open. Instruments sound like they are surrounded by a large reflective space full of air. Good reproduction of high frequency reflections. High frequency response extends to 15 or 20 kHz.
Ambience
Impression of an acoustic space, such as the performing hall in which a recording was made.
Analytical
Highly detailed.
Articulate
Intelligibility of voice(s) and instruments and the interactions between them.
Attack
The leading edge of a note and the ability of a system to reproduce the attack transients in music.
Balance
essentially tonal balance, the degree to which one aspect of the sonic spectrum is emphasized above the rest. Also channel balance, the relative level of the left and right stereo channels.
Bass
The audio frequencies between about 60Hz and 250Hz.
Bassy
Emphasized low frequencies below 200Hz.
Blanketed
Weak highs, as if a blanket were put over the speakers.
Bloated
Excessive mid bass around 250 Hz. Poorly damped low frequencies, low frequency resonances. See tubby.
Blurred
Poor transient response. Vague stereo imaging not focused.
Body
Fullness of sound, with particular emphasis on upper bass. Opposite of thin.
Boomy
Excessive bass around 125 Hz. Poorly damped low frequencies or low frequency resonances.
Boxy
Having resonances as if the music were enclosed in a box. Sometimes an emphasis around 250 to 500 Hz.
Breathy
Audible breath sounds in woodwinds and reeds such as flute or sax. Good response in the upper mids or highs.
Bright
A sound that emphasizes the upper midrange/lower treble. Harmonics are strong relative to fundamentals.
Brilliance
The 6kHz to 16kHz range controls the brilliance and clarity of sounds. Too much emphasis in this range can produce sibilance on the vocals.
Chesty
The vocalist sounds like their chest is too big. A bump in the low frequency response around 125 to 250 Hz.
Clear
See Transparent.
Closed
A closed-in sound lacking in openness, delicacy, air, and fine detail usually caused by Roll-off above 10kHz; in contrast to Open.
Congested
Smeared, confused, muddy, and flat; lacking transparency.
Coloured
Having timbres that are not true to life. Non flat response; peaks or dips.
Cool
Moderately deficient in body and warmth, due to progressive attenuation of frequencies below about 150Hz.
Crisp
Extended high frequency response, especially with cymbals.
Dark
A tonal balance that tilts downwards with increasing frequency. Opposite of bright. Weak high frequencies.
Decay
The fadeout of a note, it follows the attack.
Definition (or resolution)
The ability of a component to reveal the subtle information that is fundamental to high fidelity sound.
Delicate
High frequencies extending to 15 or 20 kHz without peaks.
Depth
A sense of distance (near to far) of different instruments.
Detail
The most delicate elements of the original sound and those which are the first to disappear with lesser equipment.
Detailed
Easy to hear tiny details in the music; articulate. Adequate high frequency response, sharp transient response.
Dry
Lack of reverberation or delay as produced by a damped environment. May comes across as fine grained and lean. Opposite of Wet.
Dull
See Dark.
Dynamic
The suggestion of energy and wide dynamic. Related to perceived speed as well as contrasts in volume both large and small.
Edgy
Too much high frequency response. Trebly. Harmonics are too strong relative to the fundamentals. Distorted, having unwanted harmonics that add an edge or raspiness.
Euphonic
An appealing form of distortion that generally enhances perceived fidelity, often ascribed to the harmonic elaborations of some valve amps.
Fast
Good reproduction of rapid transients which increase the sense of realism and "snap".
Fat
See Full and Warm. Or, spatially diffuse; a sound is panned to one channel, delayed, and then the delayed sound is panned to the other channel. Or, slightly distorted with analogue tape distortion or tube distortion.
Focus
A strong, precise sense of image projection.
Forward(ness)
Similar to an aggressive sound, a sense of image being projected in front of the speakers and of music being forced upon the listener. Compare "Laid-back".
Full
Strong fundamentals relative to harmonics. Good low frequency response, not necessarily extended, but with adequate level around 100 to 300 Hz. Male voices are full around 125 Hz; female voices and violins are full around 250 Hz; sax is full around 250 to 400 Hz. Opposite of thin.
Gentle
Opposite of edgy. The harmonics (of the highs and upper mids) are not exaggerated, or may even be weak.
Grainy
A slightly raw, exposed sound which lacks finesse. Not liquid or fluid.
Grip
A sense of control and sturdiness in the bass.
Grungy
Lots of harmonic or I.M. (Intermodulation) distortion.
Hard
Too much upper midrange, usually around 3 kHz. Or, good transient response, as if the sound is hitting you hard. Uncomfortable, forward, aggressive sound with a metallic tinge.
Harsh
Grating, abrasive. Too much upper midrange. Peaks in the frequency response between 2 and 6 kHz. Or, excessive phase shift in a digital recorder's low pass filter.
Headstage
The perception of the Soundstage while listening to headphones.
Highs
The audio frequencies above about 6000 Hz.
High Midrange (High Mids, Upper Mids)
The audio frequencies between about 2kHz and 6kHz.
Hollow
Recessed mids.
Honky
Like cupping your hands around your mouth. A bump in the response around 500 to 700 Hz.
Imaging
The sense that a voice or instrument is in a particular place in the room.
Juicy
Sound that has joie de vivre, energy and life.
Laid-back
Recessed, distant-sounding, having exaggerated depth, usually because of a dished midrange. Compare "Forward".
Liquid
Textureless sound.
Low Level Detail
The quietest sounds in a recording.
Low Midrange (Low Mids)
The audio frequencies between about 250Hz and 2000Hz.
Lush
Very Rich/Full.
Lush (2)
A "lush" sound has a sense of warmth and fullness. Notes are more authoritative and have a sense of life about them. It is a sound free of any sibilance or brightness. It does not mean colored, however. It is an open and inviting sound enveloping the listener into its soundstage. (source: unkown headfier)
Mellow
Reduced high frequencies, not Edgy.
Midrange (Mids)
The audio frequencies between about 250 Hz and 6000 Hz.
Muddy
Not clear. Weak harmonics, smeared time response, I.M. distortion.
Muffled
Sounds like it is covered with a blanket. Weak highs or weak upper mids.
Musical (or musicality)
A sense of cohesion and subjective "rightness" in the sound.
Nasal
Honky, a bump in the response around 600 Hz.
Naturalness
Realism.
Opaque
Unclear, lacking Transparency.
Open
Sound which has height and "air", relates to clean upper midrange and treble.
Pace
Often assoc. with rhythm, a strong sense of timing and beat.
Piercing
Strident, hard on the ears, screechy. Having sharp, narrow peaks in the response around 3 to 10 kHz.
PRaT
Pace, Rhythm and Timing
Presence Range
The presence range between 4kHz and 6kHz is responsible for the clarity and definition of voices and instruments. Increasing this range can make the music seem closer to the listener. Reducing the 5kHz content makes the sound more distant and transparent.
Presence
A sense that the instrument in present in the listening room. Synonyms are edge, punch, detail, closeness and clarity. Adequate or emphasized response around 5 kHz for most instruments, or around 2 to 5 kHz for kick drum and bass.
Puffy
A bump in the response around 500 Hz.
Punchy
Good reproduction of dynamics. Good transient response, with strong impact. Sometimes a bump around 5 kHz or 200 Hz
Range
The distance between the lowest and highest tones.
Resolution (or Resolving)
See Definition
Rich
See Full. Also, having euphonic distortion made of even order harmonics.
Roll-off (Rolloff)
The gradual attenuation that occurs at the lower or upper frequency range of a driver, network, or system. The roll-off frequency is usually defined as the frequency where response is reduced by 3 dB.
Round
High frequency rolloff or dip. Not edgy.
Rhythm
The controlled movement of sounds in time.
Saturation
The point at which a magnetic tape is fully magnetized and will accept no more magnetization.
Seismic
Very low bass that you feel rather than hear.
Shrill
Strident, Steely.
Sibilant (or Sibilance)
"Essy", exaggerated "s" or "sh" sounds in vocals. Sibilant sounds carry most of their energy through the 4Khz to 8Khz range, but can extend to 10kHz, depending on the individual. Sibilance is often heard on radio.
Sizzly
See Sibilant. Also, too much highs on cymbals.
Smeared
Lacking detail. Poor transient response, too much leakage between microphones. Poorly focused images.
Smooth
Easy on the ears, not harsh. Flat frequency response, especially in the midrange. Lack of peaks and dips in the response.
Snap
A system with good speed and transient response can deliver the immediacy or "snap" of live instruments.
Soundstage
The area between two speakers that appears to the listener to be occupied by sonic images. Like a real stage, a soundstage should have width, depth, and height.
Spacious
Conveying a sense of space, ambiance, or room around the instruments. Stereo reverb. Early reflections.
Speed
A fast system with good pace gives the impression of being right on the money in its timing.
Steely
Emphasized upper mids around 3 to 6 kHz. Peaky, non flat high frequency response. See Harsh, Edgy.
Strident
See Harsh, Edgy.
Sturdy
Solid, powerful, robust sound.
Sub-Bass
The audio frequencies between about 20Hz and 80Hz.
Sweet
Not strident or piercing. Delicate. Flat high frequency response, low distortion. Lack of peaks in the response. Highs are extended to 15 or 20 kHz, but they are not bumped up. Often used when referring to cymbals, percussion, strings, and sibilant sounds.
Telephone Like
See Tinny.
Texture
A perceptible pattern or structure in reproduced sound.
Thick
A lack of articulation and clarity in the bass.
Thin
Fundamentals are weak relative to harmonics. Bass light.
Tight
Good low frequency transient response and detail.
Timbre
The tonal character of an instrument
Timing
A sense of precision in tempo.
Tinny
Narrowband, weak lows, peaky mids. The music sounds like it is coming through a telephone or tin can.
Tone
The sound of definite pitch.
Transient
The leading edge of a percussive sound. Good transient response makes the sound as a whole more live and realistic.
Transparent
Easy to hear into the music, detailed, clear, not muddy. Wide flat frequency response, sharp time response, very low distortion and noise. A hear through quality that is akin to clarity and reveals all aspects of detail.
Tubby
Having low frequency resonances as if you're singing in a bathtub. See bloated.
Upper Midrange (Upper Mids, High Mids)
The audio frequencies between 2 kHz and 6 kHz.
Veiled
Like a silk veil is over the speakers. Slight noise or distortion or slightly weak high frequencies. Loss of detail due to limited transparency.
Warm
Good bass, adequate low frequencies, adequate fundamentals relative to harmonics. Not thin. Also excessive bass or mid bass. Also, pleasantly spacious, with adequate reverberation at low frequencies. Also see Rich, Round. Warm highs means sweet high
Wet
A reverberant sound, something with decay. Opposite of Dry.
Weighty
Good low frequency response below about 50 Hz. A sense of substance and underpinning produced by deep, controlled bass. Suggesting an object of great weight or power, like a diesel locomotive.
Woolly
Loose, ill-defined bass.