A Cold Open is an industry term for the portion of a television show that occurs before the theme song and/or title sequence. Also sometimes called a "teaser", a cold open is intended to capture the interest of viewers so they will sit through the credits and commercials before the rest of the show begins.
Each episode of The Muppet Show in seasons 2 - 4 would begin with Scooter knocking on the Guest Star's Dressing Room door, calling the star's name, and announcing the number of seconds remaining until curtain time. Scooter's appearance was then followed by a short quip or visual gag involving the guest star.
In season 5, the cold open was changed to show the guest star entering the theater and talking briefly to Pops.
Other Muppet/Henson have also had cold opens. Most Jim Henson Hour cold opens took place in Muppet Central, usually ending with Kermit the Frog telling Digit to start the show. Dinosaurs gained a cold open in the third season and Aliens in the Family also gained one in the second episode. Sesame Street has occasionally had cold opens (mainly during the 1990s), and all episodes since season 35 feature recurring pre-title segments which serve the same function. Muppets Tonight also had cold opens, which, unlike The Muppet Show, didn't always take place in the same location or always have the guest star.