A hiccup (also spelled hiccough) is sudden tightening of the diaphragm, which is a muscle inside the chest and below the lungs that causes air to be pulled in. A short time after diaphragm contracts, the throat suddenly closes. This closing stops the air from flowing in, and results in the "hic" sound that gives "hiccups" its name. A hiccup is a reflex, a kind of action happens in the body without trying. Hiccups often repeat several times per minute, and end on their own after a few minutes.
Sometimes a single hiccup happens, or they may happen over and over, a few times each minute, in a series called a bout of hiccups. Hiccups are rhythmic: the time between one hiccup and the next usually doesn't change much. A bout of hiccups generally ends by itself, without having to doing anything to end it on purpose. Many home remedies (cures) are often tried to attempt to shorten how long the hiccups last, because hiccups can be uncomfortable and make it hard to pay attention to other things. It is rare that medical help is necessary because it is rare that they last long enough to cause any harm.
Hiccups may be triggered (started) by several common human conditions such as swallowing air, eating very quickly, and laughing for a long time. They can also be caused by some drugs and by some diseases.
The reason that people hiccup is not known for sure. A leading theory (idea) is that hiccups evolved to help human babies and other young mammals obtain milk more easily during breast feeding. This is related to the pattern that hiccups often happen when a bubble of air forms below the diaphragm and takes up space in the belly.