Peekaboo is a simple game played with babies and toddlers where someone hides their face behind their hands or an object, then suddenly reveals it while saying “peekaboo!” The baby often squeals with delight, as if the person had actually vanished and magically reappeared.

The game works because very young babies haven't yet learned that things continue to exist even when they can't see them. When you cover your face, a six-month-old may seem to react as if you've disappeared. When you reappear, it can feel like magic. Playing peekaboo actually helps babies develop this understanding, called object permanence, which is an important milestone in how they learn to think about the world.

As an adjective, peekaboo describes clothing or fabric with small openings that reveal glimpses of what's underneath, like a peekaboo lace pattern in a curtain that lets you see through tiny holes.

As an interjection, peekaboo! is what you say when you pop into view, especially while playing the game.