On comic books and graphic novels, this is one of those things that’s a lot easier to understand than explain. Comic books are traditionally periodical publications released to a set schedule and which usually feature an ongoing series. In the US, the standard format is to release one new issue of each title on a monthly basis, to highlight one character or set of characters in each title, they run to about 20-22 pages per issue, and the convention for the last several decades has to been to have ongoing “story arcs” which play out over several issues. None of this is a requirement. A comic book can have a different publishing frequency, it can be a mini-series with a finite number of issues or even a one-off issue, it can tell a series of one-off stories to a theme rather than an ongoing story, be an anthology, and the page lengths can vary. They used to have newsstand distribution, which means you’d see them alongside magazines and newspapers, but now they are sold through the “direct market”, which usually means you have to source them from a specialised comic book retailer.

“Graphic novel” is an American marketing term. Back in my youth I used to buy “trade paperbacks”, but now everything is a graphic novel because it sounds better. AFAIK it was originally used to denote a one-off, self-contained publication in the same storytelling medium as used in comic books but published in a format similar to a novel rather than a periodical. By which I mean not stapled down the spine, thicker cover, and better quality paper (comic books at the time were printed on low quality newspaper-style paper). In the 1980s, as comic book sales were migrating from newsstands to specialised stores, companies whose business was based around selling comic book periodicals realised they could collect together chunks of previously published material into this format and sell it again. In the late-eighties, DC experienced massive critical and commercial success when they collected two mini-series in this format, The Dark Knight Returns and Watchmen. As both of these were taken seriously as literary works, “graphic novel” started to become the accepted way to refer to them because it made them sound like proper works of literature.

Since then, graphic novel has become a catch-all term for any comic book published in this format, regardless of whether the content is new or reprinted from existing comic book periodicals. As comic book sales have collapsed in the last twenty years, companies like Marvel and DC have taken to releasing material in comic books specifically with the intention of re-releasing it as a “graphic novel”. Stories now tend to last for six-issues as this provides enough content for a single graphic novel, allows each series to have a graphic novel published twice a year, and means that the reader who only buys the graphic novel has a self-contained story to read in each one. As long the comic book breaks even, the graphic novel sales provide the profit. Although even then, things have gotten so bad that if Disney and Time Warner weren’t making billions of the IPs, the comic books would have been shut down years ago.