Ice hockey rink - Wikipedia
https://en.wikipedia.org/wiki/Ice_hockey_rinkThe centre line separates the ice in half crosswise. It is used to judge icing. It is a thick line, and in the NHL must "contain regular interval markings of a uniform distinctive design, which will readily distinguish it from the two blue lines." It may also be used to judge two-line pass violations in leagues that use such a rule. There are two thick blue lines that divide the rink into three parts, called zones. …