1)  slit opening
袖侧
2)  CUFF VENT/CUFF OPENING
袖侧
3)  top vent of sleeve
大(袖)侧
4)  cuff opening
袖衩，[粤]袖侧
5)  cuff vent
(有搭位的)袖衩，[粤]袖侧