What is the term used to describe particular sound an instrument makes?

The correct term that describes the particular sound an instrument makes is called "timbre". Timbre is a French word that means "stamp" and refers to the unique characteristics of a sound that distinguish it from other sounds, even when played at the same pitch and volume. It's often described using terms like "bright," "dark,' 'warm," "harsh," "metallic," "reedy," "buzzy," "velvety," and more.