Top Ten is a generic term used to indicate the ten items that are best, worst, or otherwise notable according to some criteria. David Letterman uses Top Ten lists as a gag on The Late Show. While, by their nature, top ten lists should be counted down from 10 to 1, it is a common error to count the other way, even when parodying Letterman, who does get it right. If you count up, it's not a "top" ten list, it's merely a list of ten items. Letterman at his desk on The Late Show with David Letterman David Michael Letterman (born April 12, 1947) is an American talk show host, comedian, and television producer. ... In general terms, a Top Ten List is an ordered ranking of ten items in order of preference. ... The Late Show with David Letterman is an hour-long weeknight comedy and talk show broadcast by CBS from the Ed Sullivan Theater on Broadway in New York City. ...
Top 10 or Top-10 also refers to a variation on the Top 40record chart, often presented on radio as a countdown. Top 40 is a radio format based on frequent repetition of songs from a constantly-updated list of the forty best-selling singles. ... A record chart is a list of popular records, based on data such as sales of singles and requests to radio disk jockeys. ...