what's an elf on a shelf

An "elf on the shelf" is a popular Christmas tradition where families place a small toy elf in different locations around their home. The elf then reports back to Santa Claus at night, and each morning he returns to a new location. This is meant to encourage good behavior in children, as the elf is said to report any misbehaviors back to Santa. Some families also have the elf bring small gifts to the children each day as a reward for good behavior.