The word 背后 is formed by combining two characters that each convey a spatial concept to create a new, metaphorical meaning. The first character, 背, means "back" as in the rear surface of something, such as a person's back. The second, 后, means "behind" or "after". When placed together, they literally depict the physical area "at the back and behind" an object. This concrete image of a space obscured from frontal view is then used to express the abstract ideas of something hidden from sight or knowledge, such as behind-the-scenes activities, private motives, or talking about someone in their absence.