'Brown' - A term used by EVH to describe the perfect tonezz. Read this: http://en.wikipedia.org/wiki/Brown_sound
'tight' - Responds quickly to dynamic changes. The opposite of 'sagging,' or 'loose.' Well defined and clear. I'm sure someone can describe this better than I can. In general, solid-state amps are tighter than tube amps. This is the reason some people like them, and also the reason some hate them.
'dark voiced' - More bass and low mids than treble.
'Saturated' - Used to describe the sound made when the power-tubes become saturated with a high-level signal and clip it, producing distortion. True tube saturation sounds much different than silicon diode-clipping distortion.