To vomit means to forcefully expel the contents of your stomach through your mouth. It happens when your body decides something inside needs to come out immediately, whether it's spoiled food, too much junk food eaten too fast, or because you're sick with the flu or a stomach bug.

Your body has a complex system that protects you from harmful substances. When your stomach detects something wrong, or when you're sick, your brain triggers vomiting as a protective reflex. Your stomach muscles contract powerfully, pushing everything upward and out. It's unpleasant, but it's your body trying to help you get better.

People also use less direct words for the same thing: throw up, puke, or be sick. You might hear someone say they feel nauseated, which means they feel like they might vomit. If someone has an illness that causes frequent vomiting, doctors might describe them as experiencing emesis, which is the medical term.

Motion sickness can cause vomiting too, which is why some people get sick on boats, in cars, or on spinning carnival rides. The disconnect between what your eyes see and what your inner ear senses confuses your brain and can trigger that queasy feeling.