"Playing the same note" means they have the same pitch and loudness. For instance, timbre is the difference between a guitar and a piano playing the same note at the same volume. In music, tone quality and color are synonyms for timbre.
There are many attempts by music theorists to explain timbre more fully. Unfortunately, their ideas depend on the reader having an advanced knowledge of musical theory. The Acoustical Society of America (ASA) Acoustical Terminology definition 12.09 of timbre is "that attribute of auditory sensation which enables a listener to judge that two nonidentical sounds, similarly presented and having the same loudness and pitch, are dissimilar". It adds "Timbre depends primarily upon the frequency spectrum, although it also depends upon the sound pressure and the temporal characteristics of the sound".
- ASA Standards Secretariat (1994). "Acoustical Terminology ANSI S1.1-1994 (ASA 111-1994)". American National Standard. ANSI / Acoustical Society of America.