The term "natural" on a bottle of wine is a little like the the word "natural" on a package of steaks — essentially meaningless.

Unlike "organic" or "biodynamic," natural is an unregulated term. Both of those terms require certification, and certification requires cash. Given the expense, not all small wine producers will spring for the label. Natural, on the other hand, is free for all. That said, the purest and most correct definition is, as usual, one of the simplest:

A natural wine is one with nothing added or taken away. What might be added, you may be wondering.

Conventional winemakers use additives to create consistent results in their wines. Yeasts are cultivated and chosen to customize the flavor profile of a wine. Those nutty or banana notes you love, in other words, are the product of specific yeasts.

What's more, conventional winemakers use sulfur dioxide as a preservative in that prevents oxidation and bacterial growth. Most wines don't contain much — somewhere between 20 to 200 parts per million (dried fruit racks up 500-3,000 PPM). But sulfites in wine have been blamed for everything from hangovers to allergies to ruddy complexions. In reality, sulfite intolerance reportedly affects less than 1 percent of the population, and sorry, science says you can't blame your headache on them.

"There is no medical research data showing that sulfites cause headaches," Andrew Waterhouse, professor of enology at UC Davis, told Decanter.

But some winemakers argue sulfites can deaden the delicacy of a wine's character. And to further complicate that question of "what makes a natural wine," some natural winemakers condone the use a touch of sulfur dioxide to correct problems. In general, with or without sulfites, wines made without additives are typically described in rousing, lively terms.

Natural wines are "alive," "fizzy," and "funky." Their appearance may be cloudy, and sediment may have collected in the bottom of the bottle. Many can bear more of a resemblance to cider or sour beer than a California chardonnay.

"Natural wines can be mystifying," writes Andrea Shea at NPR's The Salt. "The first time you drink them, they may be off-putting and nose-wrinkling. They're often rough, which some people find charming. Others think they're unsophisticated."

Still, there's no denying the trendiness of natural wines, which have snagged Drink of the Year status from Bon Appetit. The millenial-geared cooking magazine highlights the wild, rule breaking impulse of the vintners behind natural wines.

"But here's what natural wine is really about," the magazine declares. "It's Elvis. It's the Sex Pistols. It's N.W.A. It's that thing your parents could never understand. Natural winemakers buck conventions and break regional rules. These wines have an undeniable energy that fills your belly and tickles your toes and sits in your soul. It's not for awarding points. It's for feeling—for feeling everything a winemaker put into it, for feeling where it takes you, and for feeling free to enjoy however you'd like."

So rule-breaking and convention-bucking are for you, ask about natural wines when you next go into your wine store. Or seek out a shop devoted to carrying natural wines. And when you encounter a natural wine on a menu or in a store, ask what makes it natural. Since the term is ambiguous, you'll want to know the specifics of how and why this wine became so deliciously untamed.