Technique
Tone
The particular quality or character of a sound.
In plain English
Tone is why the same note sounds different on a piano, voice, bass, or trumpet. Technique, equipment, touch, and the instrument all affect it.
Try or listen for this
Pluck a guitar string near the bridge, then near the neck. The pitch stays the same but the tone changes.
Why it matters
Tone helps a part communicate its character and sit well with other instruments.