A catch plate is a small 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.