I devoted some time to the factor of what I now term 'structural length" in the essay-series THE LONG AND SHORT OF MYTH, but only today decided to coin a term for the concept.
There are various accepted categories that pertain to the structures narratives take on when their authors work within certain length-specifications, and I accept the terms "vignette" and "short story" pretty much as they are regularly used. However, my study of comics convinces me to put forth my own comics-centric list of terms, to wit:
VIGNETTE-- a narrative so short that it usually consists of just set-up and resolution, of beginning and end with barely the suggestion of a "middle." THE ORIGIN OF BATMAN may be the most famous such sequence.
SHORT ARC-- this form of narrative usually does have a bit more progression, but it's clearly meant to function as part of a greater continuity, and may function as a "subplot," though it does not necessarily have to take that function. In this essay on the manga FREEZING, I mistakenly termed the two stories discussed therein as "vignettes," but I've decided that "short arc" is the better description. Just as the traditional subplot can morph into a central plotline, the short arc can develop into a longer arc.
SHORT STORY-- this is the short form best known for the traditional beginning, middle, and end. It usually has a compact structure, and can be read without reference to other stories, though such stories often appear in continuing features simply to illustrate particular situations or characters. The reader can presumably think of many stand-alone stories that conform to the paradigm, and for an example of a short-story-within-a-continuity, I'll cite SECRET OF THE MYSTERIOUS GIRL from the LOVE HINA continuity.
LONG ARC-- the long arc also takes place within a larger continuity, but like the short arc doesn't entirely stand on its own. The American "soap opera" did not originate the long arc, but it's the genre best known for particular plot-lines that could be extended for weeks, if not longer. By length alone, the long arc may be compared to the novella, though no arc can be independent of its parent continuity, as a novella can. The LOVE HINA sequence SISTER SYNDROME is my exemplar.
NOVELLA-- The novella is more expansive than the short story, but resembles the latter in being more focused than a long novel can be on a clear "beginning, middle, and end." The example here is the recent SIN CITY six-part story, THAT YELLOW BASTARD.
COMPACT NOVEL-- The compact form of the novel allows for a wider variety of plot-lines than a novella, but it is always structured to dovetail all significant plot-lines toward a satisfying resolution. This is what most people think of as a "novel," though I extend it also to serial concepts that have a similar coherence, as with Kohta Hirano's HELLSING.
EPISODIC NOVEL-- This form includes a vast number of sub-forms, such as "the romance" and "the picaresque novel." Though there's usually a unifying theme, the episodic novel does not emphasize, as the compact novel does, distinct plot-threads, but instead focuses on episodes that may or may not bear heavily upon the main plot's resolution. Melville's MOBY DICK may be the most famous example of a modern-day "literary romance," but I extend it also to serials which have thematic, albeit not narrative, unity. Jack Kirby's NEW GODS series qualifies here, and I would view it as sharing the basic structure of the episodic novel even if its creator had not been able to provide a resolution of sorts, years after the original continuity was interrupted by cancellation. Steve Gerber's uncompleted VOID INDIGO series furnishes an example of a continuity that was patently intended to function as an episodic novel, but that was doomed by overheated fan-reaction.
ADDENDUM: Just to be clear, most serial endeavors are really just assemblages of ongoing episodes with no structuring principle, usually combining short stories and long arcs. Akamatsu's LOVE HINA is not a novel, episodic or otherwise, just because the author has in mind a summary wrap-up story.