From SKYbrary Wiki
A cascade reverser incorporates radially arranged openings near the aft edge of the fan cowl of a turbofan engine. Within each of the openings is mounted a cascade set of air flow turning vanes. A blocking door and its associated actuating system are positioned flush with the inner wall of the fan cowl adjacent to each opening. The outer surface of the cascade sets are covered by a "sleeve like" translating (or sliding) section of the cowl. When the reversers are activated, the actuating system causes the translating cowl to move aft uncovering the cascades. The linkage between the translating cowl and the blocking doors move the doors into the bypass air stream blocking its normal path and diverting it out through the cascades which redirect it forward to help slow the aircraft.