Marathon television show, almost always broadcast to raise money for a charitable cause. Can run anywhere from 24 hours to a week or more of combined Variety Show and pointless filler.
The first telethon, broadcast by NBC in April 1949, was a fundraiser for the Damon Runyon Cancer Research Foundation. (In fact, NBC executive Sylvester Weaver coined the word "telethon" — a portmanteau of [...] [tvtropes.org]