Thread:1997Q/@comment-5951231-20190623200301/@comment-35682915-20190624021755

"Arc" is a really weird term. Depending on its context it can refer to a plot that takes place over multiple, not necessarily consecutive, episodes. But being part of an arc does not make an episode a multi-part, and being a multi-part episode does not necessarily make it part of an arc.

in Zi-O, the Build arc is two consecutive episodes that aren't a multi-part episode. But if we take a different show, we get arcs that last multiple seasons. In NCIS, the arc pertaining to Ari Haswari takes place over season 1 and 2, ending in Season 3 Episode 2. But not every episode is focused on him. Most aren't.(edited)

Arcs can be a way to measure "the story progressing". "The  arc" can refer to a sequence of events in multiple (sometimes consecuitve) episodes that constitute a major part of the overall story.

Most shows use consecutive episodes for an arc (Yu-Gi-Oh, for example), but not all.

On the other hand, a multi-part episode almost exclusively refers to episodes that are split into parts, i.e. Green With Evil Part I: Out Of Control.

Green With Evil is arguably an example of an arc because of how extensive that story is. The two-part first episode of Iron Man: Armored Adventures ("Iron, Forged in Fire Part 1" and "Iron, Forged in Fire Part 2") is a multi-part episode that is not an arc. That is just a long episode.