1. in imaging, a theoretical “slice” of a body or an organ (e.g., the brain) in a plane perpendicular to the dorsal–ventral axis. 2. a thin slice of tissue for microscopic study that has been cut at an angle perpendicular to the dorsal–ventral axis of the organ. A horizontal section may also be taken of an entire organ for gross examination (e.g., a horizontal section of an entire brain).