A quadrat is a frame, traditionally square, used in ecology, geography and biology to isolate a standard unit of area for study of the distribution of an item over a large area. Modern quadrats can for example be rectangular, circular, or irregular. The quadrat is suitable for sampling plants, slow-moving animals, and some aquatic organisms.

A photo-quadrat is a photographic record of the area framed by a quadrat. It may use a physical frame to indicate the area, or may rely on fixed camera distance and lens field of view to automatically cover the specified area of substrate. Parallel laser pointers mounted on the camera can also be used as scale indicators. The photo is taken perpendicular to the surface, or as close as possible to perpendicular for uneven surfaces.