Move over, cappuccino, there’s a new coffee in town. And we have the Australians to thank for it.

Flat whites are becoming the hot order at Aussie-run java joints like Culture Espresso on 38th Street, Greenpoint’s Propeller Coffee and Little Collins in Midtown. The only catch? None of them agree on exactly what this delicious drink is.

Generally, the flat white — developed in Sydney cafes in the 1980s — is defined as an espresso-based beverage that, depending on the amount of milk the barista uses, falls somewhere between latte-cappucino-cortado.

But at Propeller, which opened in May, owner Claire Spikerman admits that “strange, different arguments” surround the definition and execution. The Vancouver native, whose flat white is essentially an American cappuccino in terms of the amount of milk and presentation, learned the tricks of her trade in London from her Aussie boss there.

Meanwhile, Deaton Pigot, head roaster for Toby’s Estate, an Australia-based chain that landed in Williamsburg in 2012, likens the flat white to a “wet cappuccino” — that is, a cappuccino with more steamed milk than froth (a typical cappuccino is a 50/50 steamed-froth blend).

However, “a flat white is really a small latte,” counters Aussie Tyson Stagg, general manager of Milk Bar in Prospect Heights and the East Village’s Bluebird. “You steam the milk in the same way, so it feels like a head of freshly poured beer: light, fluffy, but not dry.”

No matter how you define it, the trend is spreading: The flat white is by far the number one off-menu item at Bourbon Coffee near Union Square (where espresso is made with steamed milk, no foam) and Ninth Street Espresso (similar to a cappuccino), as well as mini chains Joe (like a cortado, an espresso cut with a small amount of warm milk) and Oren’s (cappuccino-like).

Sure, the ex-pat factor is part of it — between 2002 and 2012, the total number of visas issued to Australians coming to the US has increased from 29,133 to 35,353. But they’re not the only ones addicted.

On a busy recent weekday morning, fashion designer Jenny Kiehl, who moved to New York from Seattle seven years ago, was ordering a flat white at Culture Espresso. An espresso and latte drinker, Kiehl worked her way through the menu before discovering the drink, now in her morning rotation. She’s such a convert, she’s even willing to insult her hometown hero: Compared to a flat white, she says, “a Starbucks latte tastes like warm milk.”