Polite form of 面 (mask), often used for festival masks, children's masks, or when speaking politely about masks.
See also: 面
The children were playing wearing masks.
striking the head (kendo)
In kendo, a valid strike to the opponent's head protector (面). The polite prefix お is often used in dojo settings.
See also: 面
In the match, he quickly landed a strike to the head.