Closed captioning is the visual representation of not only the spoken words within a video, but also text-based descriptions of non-language related audio such as music and sound effects. It's more than just a transcript. However, you may find yourself using a transcript file to create your closed captioning file.
Closed Captioning has a history in broadcast television stretching back to the early1970s. The next time you're at a party dropping useless knowledge on your friends you can use this fun fact: The first show to use closed captioning was "The French Chef" with Julia Childs in 1972.