Gluten-free this, gluten-free that. You hear the term all the time. But what exactly do the words mean when they appear on food labels?

Gluten is a protein that occurs naturally in wheat, rye, barley and crossbreeds of these grains, according to the Food and Drug Administration (FDA). Gluten can hide in surprising places, but breads, cakes, cereals and pastas typically contain it.

An estimated 3 million Americans suffer from celiac disease, an autoimmune digestive disorder related to gluten consumption, according to the FDA. People with celiac disease must be strict about their gluten consumption as any amount can trigger a reaction, damaging the small intestine.

Related: 11 Ways to Keep a Gluten-Free Kitchen

Prior to 2013, there were no standards in place for gluten-free labeling. In 2013, the FDA issued a regulation that defined the term "gluten free" and standardized the labeling of these products. To qualify, a product must contain less than 20 gluten parts per million — the lowest level that can be reliably detected in food.

According to the regulations, manufacturers that label their products “gluten-free” are accountable for "using the claim in a truthful and not misleading manner, and for complying with all requirements established by the regulation and enforced by FDA."

This gluten-free regulation applies to all foods and beverages, including packaged foods, dietary supplements, fruits and vegetables, eggs and fish. Exempted from the regulation are alcoholic beverages and USDA-regulated meat, poultry and certain egg products.

Related: Food Contamination: 6 Ways the FDA Is Stepping Up Food Safety Efforts Starting in 2016

Gluten-free products may be labeled in these four ways:

  • “Gluten-free”
  • “Free of gluten”
  • “No gluten”
  • “Without gluten”

If a food or beverage, such as bottled water or fresh fruit, is naturally gluten-free, it's not required to bear a "gluten-free" label.

The Celiac Disease Foundation suggests carefully reading the ingredients list if a product doesn't specify that it's gluten-free. Get their label-reading tips here.

Related: Hidden Food Allergens: 18 Surprising Foods (and Drinks) That Have Them

Muriel Vega is a writer with a passion for budget travel and staying safe while abroad. A Georgia State University graduate, she has over 6 years of editorial experience and has written for The Guardian, The Atlantic, The Billfold, among other outlets. In her free time, you can find her baking pies, playing with her two dogs and cat, or planning her next vacation. She spends way too much time on Twitter, one of her favorite social media channels. Her favorite safety tip: Make sure you have all the necessary shots before you go abroad.