Filler episode
Updated: Wikipedia source
A filler episode is an episode in a television series that does not progress the plot of the series. Filler episodes typically serve as filler to the overall plot, but may serve several purposes in a series; instead of focusing on the plot of a series, a filler episode may focus on the development of the characters. While not inherently "bad", they are often received negatively by viewers. Filler episodes are created for a number of reasons, depending on the series; they can be used to adjust the overall plot, or to lengthen the series. Filler episodes are common in anime, and are frequently associated with the medium. Several consecutive filler episodes in an anime can construct a filler arc.