Other forms: runaways
A runaway is a person — often a child or teenager — who leaves home. A runaway is usually unhappy at home, and most runaways have families that are desperate to find them.
A kid who grabs some snacks and hides out all night in his neighbor's tree house is one kind of runaway — a more serious runaway is a teenager who hitchhikes to a city and lives on the street or in a shelter. You can also use the word as an adjective to mean "out of control," like a runaway car rolling down a hill with no driver, or a movie that's a runaway success, making more money than anyone thought possible.