Mumps is a disease caused by a virus that usually spreads through saliva and can infect many parts of the body, especially the parotid salivary glands. The parotid salivary glands, which produce saliva for the mouth, are found toward the back of each cheek, in the area between the ear and jaw. In cases of mumps, these glands typically swell and become painful.

The disease has been recognized for several centuries, and medical historians argue over whether the name "mumps" comes from an old word for "lump" or an old word for "mumble."

Mumps was common until the mumps vaccine was licensed in 1967. Before the vaccine, more than 200,000 cases occurred each year in the United States. Since then the number of cases has dropped to fewer than 1,000 a year, and epidemics have become fairly rare. As in the prevaccine era, most cases of mumps are still in children ages 5 to 14, but the proportion of young adults who become infected has been rising slowly over the last two decades. Mumps infections are uncommon in children younger than 1 year old.

After a case of mumps it is very unusual to have a second bout because one attack of mumps almost always gives lifelong protection against another. However, other infections can also cause swelling in the salivary glands, which might lead a parent to mistakenly think a child has had mumps more than once.