In “The Film Snob’s Dictionary,” writers David Kamp and Lawrence Levi cheekily chart out the differences between Movies and Films (“It’s a Movie if it’s black-and-white because it’s old. It’s a Film if it’s black-and-white because it’s Jarmuschy.”) They might have added another definition: It’s a Movie if it ends. It’s a Film if it stops. ¶The ambiguous ending has long been one of the hallmarks of the classic art-house film, as reliable a convention of independent filmmaking as guns are to Westerns or fireballs are to action spectacles. (Granted, once in a while a mainstream blockbuster will leave audiences hanging: Was Leonardo DiCaprio still dreaming at the end of “Inception”?) ¶This year alone, filmgoers have been provoked (or infuriated, depending on their need for closure) by several non-ending endings: In Kelly Reichardt’s “Meek’s Cutoff,” the band of 19th-century settlers whose trek she methodically follows are on the verge of deciding which path to take just as the movie ends. In “Take Shelter,” Jeff Nichols’s insinuatingly creepy

drama about a man who may or may not be preparing for the apocalypse, an epilogue leaves viewers more uncertain than ever whether it was all in his head.

And in “Martha Marcy May Marlene,” opening Friday, writer-director Sean Durkin leaves the eponymous multi-monikered protagonist similarly in the lurch, with Elizabeth Olsen’s title character literally on a road that could end in disaster or the shaky promise of a new life.

The indeterminate final scene of “Martha Marcy May Marlene” is a textbook study in the inconclusive conclusion, which has produced a rhetoric all its own among the actors and filmmakers on publicity tours, hoping to break audiences of their addiction to the happy — or at least final — ending. “The movie begins in a transition from one place to another, and it ends in transition from one place to another,” Olsen told The Post’s Monica Hesse last week. “We go to movies because we want to see wrapped-up stories, but our whole lives are nothing but transitions — people don’t want to accept it [on-screen], but that’s how we are every day.”

Okay, we get it: Rocky doesn’t always win, the shark doesn’t always die and Dorothy doesn’t always get back to Kansas. Life is messy! Art imitates life! But that doesn’t help us with the essential questions: What does Bill Murray say to Scarlett Johansson at the end of “Lost in Translation”? Will Mickey Rourke be okay at the end of “The Wrestler”? What the frickety-frack was up with that storm at the end of “A Serious Man”? (Blame the Bible for that one, folks.)

And, perhaps most confounding: When is a non-ending ending a legitimate artistic choice, and when is it just a cop-out? The answer lies in how effectively a filmmaker creates characters whom viewers are willing to care about and identify with — to the point of being willing to join them in perpetual limbo.

Ambiguous endings may provide toothsome fodder for chat boards, DVD extras and satirical Web videos. But they’re serious business, entailing their own rules that filmmakers break at their peril. Unless they’re Christopher Nolan, for example, no director is allowed to use the “It was only a dream” gambit. And even he wasn’t born with the privilege: His run-in-reverse breakout film “Memento” was more style than substance, inducing a shrug of indifference rather than genuine intrigue.

Similarly, as masterful a stylist as Martin Scorsese couldn’t pull off the ambiguous ending trick in “Shutter Island,” which was too tonally uneven and multi-focused to make viewers identify deeply with whether Leonardo DiCaprio’s character was framed or insane. And, if the lack of resolution was appropriate to the Coen brothers’ adaptation of the Book of Job in “A Serious Man,” the kinda-makes-you-stop-and-think speech they gave Tommy Lee Jones at the end of “No Country for Old Men” made their chilly genre exercise only all the more mannered and pretentious.

Indeed, “No Country for Old Men” epitomizes why ambiguous endings have become such an indie cliche, the index not of a filmmaker’s skill but of his contempt for his audience. (With every one of Jones’s long-drawled syllables you could almost hear the Coens congratulate each other on creating the foolproof test of who was sophisticated enough to “get it.”)

Then again, preciousness lies just as often in the eye of the beholder. If you were mesmerized by the immersive experience of watching “Meek’s Cutoff,” the dilemma in which Reichardt left her protagonists — and, by extension, the audience — felt chillingly right-on. If you thought it was a stultifying slog about women in bonnets, eh, not so much. But even the film’s detractors couldn’t argue that the final moment wasn’t earned.

“So much of the movie is about people making decisions without enough information,” said “Meek’s Cutoff” screenwriter Jon Raymond at the Sundance Film Festival in January, adding that the film was largely driven by “an unknowable element at the center of the story that allows the drama to happen. To close that off with a great resolution is almost like [missing] the point of the way we’ve constructed it. It’s very much about that ongoing confusion.”

Of all the non-ending endings this year, by far the most effective has been the epilogue of “Take Shelter,” which follows a scene that viewers first take to be the finale and leaves them unsure of what’s reality and what is a hallucination. Either way, Nichols knew that he had to include a moment between the central married couple — played by Jessica Chastain and Michael Shannon — when they look at each other and silently acknowledge that they’re seeing the same thing.

“It can be left ambiguous as long as a moment inside of that ending is specific, which is when these two characters look at each other,” Nichols said at the Toronto International Film Festival in September. “That has to be clear. If I miss that, then anybody can say this movie . . . didn’t fulfill its promise. [But] as long as that’s intact, you’re free to interpret the end however you like.”

In other words, Nichols meticulously followed the rules of the non-ending ending, creating characters the audience roots for and wants to stay together, whether in reality or each other’s dreams.

Another rule? Never tie things up so completely that you leave yourself no options. At the end of “Drive,” Ryan Gosling’s getaway-car driver suffers a stab to the gut that in any town but Hollywood would surely be fatal. Audiences may quibble whether he’ll live or die on the road, but for director Nicolas Winding Refn, the ending is anything but ambiguous. “Oh, he lives! Absolutely!” Refn said during a visit in September. “So there may be a ‘Drive 2’!”