A Cubemap is a collection of six square textures that represent the reflections on an environment. The six squares form the faces of an imaginary cube that surrounds an object; each face represents the view along the directions of the world axes (up, down, left, right, forward and back).
Cubemaps are often used to capture reflections or “surroundings” of objects; for example skyboxes and environment reflections often use cubemaps.