Among television shows, many tell a single story from beginning to end, from the start to its full conclusion, within a single episode. Some spread that single story over two or more episodes: The set of episodes over which a single story is told can be referred to as an arc.
This same usage is also seen in comic books or graphic novels.
From
Story arc - Wikipedia :
A story arc (also narrative arc) is an extended or continuing storyline in episodic storytelling media such as television, comic books, comic strips, boardgames, video games, and films with each episode following a dramatic arc. On a television program, for example, the story would unfold over many episodes. In television, the use of the story arc is much more common in dramas than in comedies, especially in soap operas.