A catch plate is a small steel plate welded to either the latch stile of the gate or the latch post of the frame. It does two jobs at once. It physically stops the gate over-swinging past closed (you don't want the leaf hitting the post past where the latch can engage). It also gives the latch tongue a flat target to land on.
Common sizes are 50 to 100 mm long, 30 to 75 mm wide, and 4 to 8 mm thick, depending on the gate weight. The plate sits on the inside face of the gate (back/property side) so it isn't a kicking target from the street.
CAD60 surfaces a catch-plate option per gate model with width, height, thickness, mount face (front/back), and weld target (latch stile vs latch post) all configurable. The plate appears on the front-elevation drawing with its own dimension callouts.