Bright:  Emphasis on high-frequencies, specifically upper-mids with emphasis on harmonics.

Crunchy:  Exists between 2K and 4K, typically distortion based and generally pleasant.  Can lend rhythmic distinction to distorted rhythm parts.

Detailed:  Minutiae of the music are easily audible.  Present sounding, intimate and close with lots of articulation and transient response throughout the upper mid range.

Forward:  Present, in your face.  Detail present in transients and upper harmonics which lends a feeling of proximity.

Glassy:  Brittle sounding, too much upper-mid content especially with regard to harmonics in relation to fundamentals. 

Grungy:  Lots of distortion with emphasis on odd harmonics.

Hard:  Excellent transient response combined with an overemphasis on upper-midrange frequencies.

Harsh:  Peaking in the 2-6 KHz range.

Metallic:  Emphasis on upper-mid range frequencies, specifically those that deal with odd order harmonics in this range.

Pinched:  Narrow-bandwidth, often relegated to the upper-mid range frequencies.  Try boosting lower frequencies to balance.