A hitchhiker is someone who travels by standing beside a road and getting free rides from passing drivers. The hitchhiker typically holds out their thumb (called thumbing a ride) to signal that they need transportation. When a driver stops, the hitchhiker explains where they're going, and if it's on the driver's route, they hop in.

Hitchhiking was common in America from the 1930s through the 1970s, when travelers, college students, and people without cars would thumb rides across towns, states, or even the whole country. It was seen as an adventurous, economical way to travel. You'd see hitchhikers along highways with backpacks, holding cardboard signs showing their destination.

Today hitchhiking is much less common in the United States, partly because more people own cars and partly because both drivers and potential hitchhikers worry about safety. Many parents specifically warn their children never to hitchhike or pick up hitchhikers.

The word can also describe something that catches a free ride without asking. Scientists talk about seeds that are hitchhikers, catching rides on animal fur to spread to new locations. In computer programming, a hitchhiker might be an unexpected piece of code that tags along with a software update.