When a TV or radio station plays a show again, after its first broadcast, that's a rerun. You may have grown up watching reruns of the shows your parents loved when they were kids.
Use rerun as a noun, for the show itself, or a verb, to describe the process of rebroadcasting it: "They rerun this movie every year at Christmas time." When someone used this word in the early nineteenth century, they were talking about races being rerun, or run again. It was first used to mean "television rebroadcast" around 1955.