The fashion season called resort has had a few lives. For a good part of this century, it was everything the word connotes, which is to say, leisurely maillots and caftans to fill the steamer trunks of wealthy women sailing off for winter holidays. In more recent decades, it served as a sort of retail caulk with tried-and-true basics filling in the cracks on shop floors between fall sales and spring arrivals. But it’s the latest incarnation that the fashion industry can’t stop talking about. Like Clark Kent after a visit to a phone booth, resort has gone from mild-mannered and meekly helpful to a seasonal superpower on which luxury labels depend for strong retail sales and even a dash of prestige. It’s a colorful irony that a season inspired by leisure time has become the hardest-working collection in the business.

“Most of the collections [in the late ’80s and early ’90s] were not terribly fashion-oriented,” Saks Fifth Avenue president Ron Frasch recalls. “Many times the designer didn’t even do them. It was the team. They tended to be things that had performed in the prior season but in different fabrics.”

These days, however, the most “wearable” collection bridges the two main runway seasons and can account for up to 70 and sometimes 80 percent of women’s designer-apparel sales. “Resort has become an independent fashion season that will oftentimes rival a spring or fall,” says luxury consultant Robert Burke.

Coupled with a shifting identity, resort—also known as cruise and pre-spring—has found itself with a handful of monikers along the way. “Resort?” says Stella  McCart­ney. “How unsexy is that word? It feels so dated. We call it spring.” Oscar de la Renta CEO Alex Bolen has another suggestion: “They should call it November delivery. These are not really clothes that go to a resort.” Michael Kors has raised the white flag of surrender. “I’ve given up on renaming it,” he says. “We’ll call it the little season that could.”

Conceived to be refreshing and commercial, resort tends to be more wearable than runway collections, without so many of the “Who would wear that?” moments. But this distinctly retail bent meant the clothes were largely ignored by fashion magazines. You can credit Karl Lagerfeld with leading the charge on turning the tide. Last May, the Chanel creative director set his resort 2011 show against the fabulous backdrop of Saint Tropez’s harbor. Models arrived by speedboat as the sun was setting. Famous and beautiful friends of the house like Vanessa Paradis, Leigh Lezark and Diane Kruger were flown in for the occasion.

This was actually Lagerfeld’s 11th resort spectacular. His first, in 2000, was staged at Paris nightclub Régine. “Karl was visionary. He was the first one to perceive the growing importance of the cruise collection,” says Chanel’s president of fashion, Bruno Pavlovsky. Although transporting a group of international journalists and the rest of your chic posse everywhere from Venice to Miami is not a cheap proposition, Pavlovsky adds: “Chanel is very attached to the way we show this collection.”

In the past few years, it seems that every designer became hyperaware of resort’s particular advantage of a selling period that can stretch from late October until June, encompassing high-volume holiday-shopping periods, and is marked down at the same time as spring runway clothes (resort has the longest window before being marked down, most commonly November to May at full price). It’s only logical to make the most of it. Also joining Chanel were Oscar de la Renta and Christian Dior with runway presentations that couldn’t be ignored. In 2006, Style.com added resort coverage to its database of fall and spring runway reviews.

Nowadays, not every label does an extravaganza, but there’s still great care taken with the presentation. Most European designers fly in to meet and greet, like Stefano Pilati, who staged Yves Saint Laurent’s resort show this year at the French consulate in New York. McCartney showed hers at a downtown gallery over margaritas and vegetarian hors d’oeuvres; in attendance were A-list friends like Gwyneth Paltrow and Naomi Watts. Meanwhile, Lanvin’s Alber Elbaz has chosen to work his considerable charm by personally narrating multiple minishows for small groups of editors and retailers.

The younger guard has followed suit, even though adding another collection to a small team’s production cycle is daunting. Los Angeles–based designer Juan Carlos Obando did his first resort collection this year. “I was extremely concerned because resort happens right when you’re trying to produce the fall show and it has to be delivered right when you start producing the spring collection,” he says. The gamble paid off. Barneys ordered double what they had from his fall 2010 show. Michelle Obama favorite Jason Wu has done a show for the past two seasons. “Why shouldn’t it be [as important]?” Wu says. “The numbers are just as great as the main seasons.” Actually better. Wu reports that he sells 60 percent resort to 40 percent runway. This season, Wu took the collection to Paris to show to European stores and ended up adding 30 new accounts.

It all adds up to the fact that designers are making these clothes a high creative priority—but within the confines of the original customer-friendly intention of the season. It’s a combination that results in a sort of perfect fashion storm. “It’s more of a realistic collection,” says Laura Vinroot Poole, owner of Capitol boutique in Charlotte, N.C., who has consistently channeled her budget heavily into resort. “They’re just beautiful clothes, rather than the sort of idea that’s been gone over and over with stylists.”

But in today’s flat fashion world of online shopping, perhaps the season’s biggest asset is simply that it’s yet another delivery of clothes. “[Resort] really supports our customers’ desire for newness,” says Net-a-Porter’s vice president of marketing and sales, Alison Loehnis. Loehnis reports high double-digit growth in the company’s resort sales over the past four years.

Even for bricks-and-mortar businesses, resort’s wide-ranging product that includes outerwear, knits, fur and lightweight early-spring clothes satisfies the current trend of buying clothes for immediate consumption that is especially important post global economic crisis.

And as the industry continues to recover from the doldrums of 2009, customers will increasingly be seeing ad campaigns to support these collections. While many houses—Prada, Bottega Veneta and Donna Karan included—did resort-specific advertising in 2008, the numbers logically dropped off afterward. Louis Vuitton and Michael Kors are the rare brands that have been consistent in this arena. De la Renta’s Bolen says, “I would say for us, it’s coming very soon.” Considering that the company sells more units of resort than of any of its four deliveries, it’s likely very, very soon. As Kors sums up, “This is when people are in stores. Treating [resort] as a stepchild in any way whether it’s advertising, design or even quantity is foolish.”