BBS posed an interesting question regarding defining tone. Unfortunately, many responses appeared to be statements of favorite or non-favorite guitarist's sound.
I put forth the following definition:
Tone is the interaction between frequencies of a percieved guitar sound.
The perceived tone of a guitarist results from two main parameters: 1) the sound produced by the guitarist's equipment, including techniques used to record the guitarist, and 2) the guitarist's technique.
Both parameters are multi-faceted. For example, equipment can include the guitar (including strings, pickups, wood, etc.), the preamp, effects, speakers, mics, mic placement, mic preamps, recording medium, and placement in the mix, etc. The guitarist's technique can include pick attack, timing, vibrato style, tricks (hammer/pull offs, tapping, sweeping, etc.), etc. All of those factors are involved in a perceived guitar sound.
Quite often when we discuss "tone," we are refering to the way a piece of equipment sounds. When we are referring to the way it sounds on another guitarist's album, it is difficult to separate the equipment (and all its facets) from the playing style.
Otherwise, we are referring to how the equipment sounds when we are playing through it. In this case, playing style is constant, and we are referring to how we perceive our sound while playing through a piece of equipment. Thus, the "tone" can include not only the frequencies (including harmonics and overtones), but also the way the equipment reacts to our playing.
I pose this definition because in my ongoing quest for the ultimate guitar tone, one overriding factor is how a piece of equipment "reacts" to my playing. I.e., if my subtle variations in attack produce discernable tonal variations. In fact, this past weekend, I went to a shop looking for a quick piece of equipment for a jam session. I finally found a salesman/guitarist that volunteered this definition (the way the amp reacts to playing) in characterising an amplifier. I was so impressed by his approach and his attentiveness, I bought a piece of equipment if only to make sure he received some of his commission for his efforts (he stayed a half hour after the shop closed to A/B equipment with me).
Matt