trifocal

This term is primarily used in optometry and ophthalmology to describe a specific type of corrective lens. It is a technical descriptor that distinguishes a lens from bifocals (two focal lengths) or single-vision lenses. While it functions as an adjective to describe the property of the lens, it is frequently used as a noun in clinical or retail settings to refer to the eyeglasses themselves.

In common usage, trifocals are often grouped under the broader category of progressive lenses, though they are technically distinct because trifocals have visible lines separating the three zones. When used as a noun, the word typically refers to the entire pair of glasses rather than a single lens.