The word’s root means “set apart.” The sacred is the place, object, time, or act marked off from ordinary use and set into relation with what is deeper than ordinary use.
Mircea Eliade distinguished the sacred from the profane not as good from bad but as different modes of attention. The sacred is where the world is felt as transparent to something more — a tree, a river, a temple, a meal eaten slowly. Every tradition builds containers for this mode and rites for entering and leaving it.
Much of the modern condition is a loss of the sacred as a distinct mode. Some argue this is why so many search for it elsewhere — in art, in nature, in occasional glimpses of what used to be common.