An episode of a TV series in which the plot revolves around a boring or unloved side character. This term comes from a Family Guy episode in which the main character, Peter Griffin breaks the fourth wall and makes a reference to the phenomena by apologetically informing the audience that this was to be another "Meg episode".
Friend 1: Oh great! A new episode of Widgets!
Friend 2: Sorry man, I already downloaded it. It's a another Meg Episode, all about John Doe. Boring.