It maps where objects belong in stereoscopic 3D space.
Dense disparity maps (depth maps) are grayscale images that determine the Z depth placement of each pixel in a 2D image. The concept is equivalent to Z buffer maps in CGI animation. Objects closer to camera are rendered closer to 100% white and infinity is rendered as pure black.
A depth map can be used in conjunction with complimentary full color 2D image for a variety of stereoscopic post production processes. For example, a depth map can be used to create additional multiscopic views.