A flute and a violin playing the same pitch at the same volume still sound different because of timbre: the mix of overtones, the attack and decay of the note, and noise in the sound. Timbre is why a felt piano sounds soft and a bright grand sounds crisp.
In production, timbre is shaped with instrument choice, playing technique, EQ, distortion and effects.
Using it in a prompt
Describe timbre with sensory words: "warm", "breathy", "glassy", "gritty", "muted". These often change a result more than naming a genre.