Advent calendar 
noun
A piece of card incorporating small numbered flaps, one of which is opened on each day of Advent to reveal a picture appropriate to the season.Shoppers are becoming immune to the annual invitation to spend all their cash before the first window on the Advent calendar has been opened....
- Concealed doors and traps tend to fly open unexpectedly like windows on an Advent calendar.
- About half the population will listen to or view the Queen's speech, buy a Christmas tree and have an Advent calendar hanging in the house.