Telethon

Cartoon characters standing by to take your pledge!

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 "television" and "marathon"—to describe the program, which was a radically different event that he hoped would entice people to buy TV sets.) The Foundation's first big fund-raiser, the telethon ran a then-unprecedented 16 hours with Milton Berle as its host, and raised $100,000. In all ways it was more or less indistinguishable from "modern" telethons, from the stars and celebrities who performed and urged donations, to the big on-screen bank of telephone operators taking calls.

Not to be confused with the film Telefon.

Examples of Telethon include:

Film

The Muppets has the titular characters running a telethon in an attempt to buy back their studio.
In the film, Americathon, the country had to hold a 30 day telethon to repaid its debts or risk foreclosure.
To raise funds in order to buy the station, Weird Al holds one at the end of UHF.

Live-Action TV

Joey is one of the people answering the phones in an episode of Friends.
Parodied in Seto no Hanayome, when Lunar starts up a Telethon for Mikawa when everybody thinks he's dying.
In one episode of Newhart, Michael convinces Dick to host a 72 hour telethon for the TV station that they work for—despite that it is a commercial station and not PBS.
On Family Ties Steven Keaton is working a PBS Telethon when his snowbound wife goes into labor.
On an episode of The Simpsons Homer flees the country after welshing on a large PBS donation he made to get them to end the telethon.
Jerry Seinfeld works the WNET Channel 13 Telethon in the episode in which his Nana goes missing.
The Robot Chicken telethon always tends to end with everyone dead.
On American Dad, the CIA loses funding for torture, so they hold a telethon to raise funds for it.
In one rather silly G.I. Joe episode, Cobra has a telethon to gather the funding they need for their next criminal operation from other crooks.
In Phineas and Ferb, Dr. Doofenshmirtz hosts a "Telethon of Evil," which hilariously gets mistaken for satire by Lawrence Fletcher.

Dr Doofenshmirtz: "I want your money, I'm strapped for cash! I need your money, too lazy to get a job."

Real Life

The most famous would be Jerry Lewis's Muscular Dystrophy Telethon.
Britain has Comic Relief and Children in Need. One example of the latter had half of The BBC's news team dress up as Duran Duran and sing "Wild Boys". The most recent example involved a James Bond spoof with the entire team (and Roger Moore).
Every October, Perth hosts the Australian Telethon (simply known as 'Telethon') to raise money for sick kids. And for the last 10 years it has exceeded the 1 million dollar mark, with the current record being 6.5mil last year.
In Norway, this is done by the NRK, the Norwegian State Broadcaster, every October. The money goes to different good purposes each year, which is promoted weeks in advance. In addition to being a telethon, volunteers go door-to-door and ask for donations on the same day the telethon is held.
Ever since The Seventies, Chilean public TV channels host the Chilean Telethon almost every December to donate for the "Sociedad de Ayuda al Niño Lisiado" (roughly translated as "Crippled Children Aid Society"), raising money for crippled kids. This is said to be the inspiration for Jerry Lewis's Muscular Dystrophy Telethon; whether it was the case of not, it did doubtlessly inspire many other telethons across Latin America.
ABC Family is required to air a CBN telethon every year the last Sunday in January; this was one of the sale conditions CBN owner Pat Robertson put in his contract to sell the network to Fox in the late 1990's, along with keeping three hours of ABC Family airtime per day.
Once a Season the Non-Profit The Funday Pawpet Show holds a telethon/auction to raise money for creator Yappy's operating expenses and music licensing costs.
Not technically a telethon, as it's not aired on television, but Loading Ready Run holds "Desert Bus for Hope" every year to raise money for Child's Play.
The most infamous might be pledge week on public television, a regular occurrence on most PBS stations (which rely heavily on viewer donations). Usually referred to as "pledge drives", these disrupt regular content up to four times a year with special programming interrupted by repeated fund-raising breaks. Thank You.
National Public Radio is also prone to beg for donations from listeners to remain on-air.
WTBS 17 Atlanta, in its early days as a UHF independent Struggling Broadcaster, crossed this line at one point in a desperate attempt to stay on-air. Unusual for a real commercial station, although "Weird Al" Yankovic does this with a fictional U-62 in film. Hilarious in Hindsight as the station was uplinked to satellite in the late 1970s and is now prosperous.