The brightest parts of a scene that yield texture or image information. With slide film, it's best to bias expose for the highlights, as overexposure of bright areas will yield a burnt-out look. A spectral highlight is pure light and will print as "paper" white.
Small, very bright part of image or object. Highlights should generally be pure white, although the term is sometimes used to describe the lightest tones of a picture, which, in that case, may need to contain some detail.