what does the elf on a shelf mean

The Elf on the Shelf is a Christmas tradition where a small elf doll is placed in a household to monitor the behavior of children. The elf, named "Elfie", is said to report back to Santa every night about the children's behavior and to ensure they are being good. The Elf on the Shelf is typically placed on a shelf, windowsill, or other elevated location, and is moved around each day to surprise the children. Elfie is also said to leave notes, treats, or other surprises for the children to find.