Filler

In television, filler are the 'unimportant' episodes in a continuity-based series that are not required to understand the basic story arcs. However, they are sometimes used to give background to characters and events, or chances for writers to show off creativity and deviate from the standard mood. Filler is tolerated to certain degrees by fans, so long as it does not contradict the main storyline.

The most common filler is a Character Episode which focuses on a single backstory of motivations of one character. These are useful in series which have large casts.

The term probably originates from the prejorative use of unecessarily padding out a weak story, especially if viewers feel there are of poor quality. Filler is more apparent in series which producers are demanded to have specific episode counts per season.