noun
: a mode of perception induced by some character of an object that does not coincide with the perception itself
such qualities, which in truth are nothing in the objects themselves, but powers to produce various sensations in us by their primary qualities, i.e. by the bulk, figure, texture, and motion of their insensible parts, as colors, sounds, tastes, etc., these I call secondary qualities — John Locke
— contrasted with primary quality and tertiary quality