normal course; proper course; regular way
A formal noun for the normal, proper, or expected course of action or conduct. In modern usage it is especially common in negative or deviation expressions such as 常軌を逸する.
His remarks are beyond the bounds of normal behavior.
After the confusion, operations finally returned to their normal course.
普通 is the everyday, casual word for ordinary or normal, while 常軌 is a formal, abstract term mainly used in phrases about deviating from normal conduct.
A Sino-Japanese compound: 常 means usual or constant, and 軌 means track, rule, or course. The spelling transparently matches the sense of a usual or proper course.