Leader

A film leader is a length of film attached to the head or tail of a film to assist in threading a projector or telecine. Leader attached to the beginning of a reel is sometimes known as a head leader, or simply head, and leader attached to the end of a reel known as a tail leader or foot leader, or simply tail or foot.
A universal film leader is a head leader designed for both television and theatrical motion picture exhibition applications. This not only includes the countdown, but technical information about the film, including, but not limited to title, studio, production number, aspect ratio, sound level and mix, reel number and color.
Head leaders are marked with visual and audio information that may be used to ensure that the correct amount of time is allowed for the machine to run up to speed and arrive at the beginning of the program or movie. They generally feature a countdown.