"In Media Res" (literally "In the Middle of Things) would be a term used for any story that starts at some point in the plot that is not "ab ovo" (Trans: The beginning, Lit: From the Egg) and requires the readers to press forward in the narrative to find out what happened just prior to the beginning, while "ab ovo".
A work is said to be a "Non-Linear Narrative" if it relies on events occurring out of order. "Arrow" is speciffically listed on Wikipedia as an example of this form (sorry @Thom, the term exists).
It should be pointed out Non-Linear Narrative does not mean parallel. The novel (and film) "Holes" start "In Media Res" and the part of the story that is before the book begins are also "In Media Res" to two seperate events that could both be "Ob Ovo" as they introduce two historical characters that are unrelated to the plot (the main character's great-great grandfather, and Kate Barlow, who existed in two non-contemporaneously periods of history... the great-great grandfather is from early 1800s eastern Europe and Kate Barlow is from 1885 Texas.). Told linearly, the main story is the conclusion to two different beginning stories that have little bearing on either.
Similarly, Star Wars (aka a New Hope) starts "In Media Res" to two different "Ab Ova". The opening scene with the space fight is immediately "In Media Res" to the "Ab Ovo" of "Rogue One" which ends immediately before the opening of A New Hope, but as the first entry into the franchise, is also "In Media Res" to the Epic Serial of the Star Wars films. If one accepts A New Hope as a stand alone story, then it could be argued that its also an "Ab Ovo" story as well, since the film properly starts the story from the beginning (A long long time ago in a Galaxy far far away... cue the John Williams) and the briefest summation of events immediately prior to the film's visual start is presented in the opening crawl. While characters drop lines that hint that this is but one bit of history in a larger history of the story, that history is sufficiently filled in linearly when limited to watching just the one film. The references to the Imperial senate, the Clone Wars, and Jabba the Hutt, are not needed to understand the story that starts in Leia's ship and finishes with Han, Luke, and Chewbacca being decorated by Leia before the Rebel Alliance.
Televison will often have a unique form of "In Media Res" that also is not parallel. These stories start "In Media Res" with a shocking to the audience event and then will flash back immediately to the "Ob Ovo" of the story and progress linearly to the point of the "In Media Res" start, which is usually the conclusion of the story. In the Firefly episode "Trash", for example, the first scene is of Captain Mal, alone in the desert, naked as the day he was born, quipping, "Yeah, that went well." The scene flashes back and the story continues. Breaking Bad's pilot episode takes it one step forward: We open on Walter White driving the RV into a ditch, pulling off his enviromental suit and grabbing a gun, and walking outside the RV as sirens approach. We then cut to a flashback which builds the story to the opening "In Media Res" where the viewers learn the conclusion to the the cliffhanger start of the episode... is also a cliffhanger for the entire episode. The next episode opens with the real conclusion to the events of the first, which are that the sirens are from a fire truck responding to a fire further down the street and not the police Walter was fearing.
The TV series "Heroes" and "Doctor Who" both feature episodes that are both "ob ovo" and, "In Media Res" and Linear storytelling at the same time. It helps that in both series, time travel is possible. The easier one is Heroes, in which episode 2 opens immediately after Hiro teleports from Tokyo to Time Square, but the entire episode is non-linearly told. The audience, and Hiro, only learn this at the end of the episode, that Hiro "teleported" to New York in an instance from his perspective only. To the rest of the world, it took Hiro 6 months (as he is a time traveler and he accidentally jumped to the end of the season). It is linear in that we are shown the story as it progresses, but is non-linear as much of Hiro's story is told parellel to characters who are progressing linearly in Hiro's Past, and another Hiro from Five Years in the future tells one of theses "past" characters about a future disaster before the present Hiro even meets the other character... or even learns of the disaster.
Doctor Who has two characters who's love story is "ab Ovo" and "In Media Res" at the same time. The Doctor and the character River Pond are both time travelers and because of this, the Doctor and audience first meet River on the day she dies, and she behaves as if they were life long friends and produces knowledge of the doctor that no stranger would know, indicating a personal relationship with him where as in the linear progress of the show, he's never seen this woman in his life. When he asks her as to how she knows him, she responds with her catchphrase, "Spoilers" because the events surrounding their first encounter would change if he knew what was going to happen. The actual episode that reveals this isn't seen for another two seasons and at this point, flips the dynamic. Up until the second "first encounter" River knows more about the Doctor's future then he does, and hides it. After the encounter, the Doctor now knows more about River's future, and hides it. Essentially, prior to the reveal, The Doctor is still learning about River who acts like they have been in love for ages, while after the reveal, the doctor acts as if they have been in love for ages, while River is still learning who he is. Somewhere in the middle of all of this, they both start keeping diaries of their encounters, specifically so they know what they can and cannot reveal to each other (River's diary was actually introduced in her introduction episode. The Doctor's lack of a Diary clues River to the fact that this is her "last" Adventure, as by this point in her story, she knows he met her on the day she dies, and his complete lack of any recognition of their traditions means she's encountering him long before he's established some knowledge of her at all.). The day she knows everything she will ever know about him, is the same day he knows nothing about her.