the back or behind: the rear of something, the direction backward, and (of time) what is still to come
At its core this word points to whatever is behind. It can name the rear side of a physical thing (the back of the tabernacle, the hindquarters of the bronze oxen, even God's back), or the region simply at one's back, as when a person is hemmed in behind and before.
Most often it describes motion in reverse. In the Psalms and the prophets, to be turned back or driven back is the standard picture of an army routed in battle or of people who have turned away from God. So the plain direction backward usually carries the weight of defeat, retreat, or falling away, not just which way someone is facing.
Hebrew also lays out time along this same front-and-back line, but the reverse of the English way. The past is thought of as in front, already seen, while the future is behind, out of sight. So this word can name the time still to come, which is why a couple of passages use it for things that are going to happen rather than for a place.