shower pans have a curb (a small step) on the entrance side and three splash walls.
Left & Right Dual curb
shower pans have two curbs, one on the entrance side and a second on a side adjoining the entrance; the other two sides have splash walls. Typically used for corner showers.
shower pans have three curbs, one on the entrance side and a second and third on each of the two sides adjoining the entrance; the fourth side (opposite the entrance) has a splash wall.
shower pans have no curb so the entrance is totally smooth for a roll-in or walk in access.