Pareidolia is the tendency to look at a random shape or pattern and imagine you can see a specific, familiar object in it. If you perceive a smiling face in an electrical outlet, you've experienced pareidolia.
Humans are wired to make sense out of randomness, and pareidolia is one example of this. Anyone who's spent a summer afternoon finding dinosaurs, race cars, and rabbits in the clouds overhead can understand this phenomenon. Some people's brains are especially inclined to pareidolia, quick to see human faces in signs, cars, houses, or even grilled cheese sandwiches. Pareidolia is derived from the Greek para, "beside," and eidos, "images."