The elf on the shelf is a popular Christmas tradition where a small toy elf is placed in a child's home to keep an eye on their behavior and report back to Santa Claus. The elf has magical powers that allow it to move around the house without being seen, and the child is encouraged to treat the elf with kindness and respect. If the child misbehaves, the elf may move to a different location to send a message that they're being watched. On Christmas Eve, the elf returns to the North Pole to report to Santa.