If you could turn a four-point polygon into a light, you’d have an Area light. Light is sent out equally in all directions, except along the edges. This type of light might be used for flat light panels or as a portal light to bring GI samples inside a room.
Unlike the Distant, Point, and Spotlight lists, you can size these lights, just as you would an object. Another distinction is that ray-traced shadows will have physically accurate edges that are sharpest near the object that is casting them and get softer further away. A smaller area light will result in sharper shadows than a large area light.