An Advent calendar is a special calendar which is used to count or celebrate the days of Advent in anticipation of Christmas. Some calendars are strictly religious, whereas others are secular in content. Despite the name, most commercially available Advent calendars begin on December 1, regardless of when Advent begins, which can be as early as November 27 and as late as December 3.
Today, most Advent calendars are made for children. Many take the form of a large rectangular card with "windows" of which there are often 24; one for each day of December leading up to Christmas Day. One is opened every day during Advent. In many of these calendars, each window opens to reveal an image, a poem, or a portion of a story such as the story of the Nativity of Jesus. More elaborate Advent calendars have a small gift concealed in each window, such as a toy or a chocolate item.