A round trip is a journey that goes to a destination and then returns to the starting point. When your family takes a round trip to visit relatives in another city, you drive there and drive back home again. Airlines sell round-trip tickets that include both the flight out and the flight back.

The term emphasizes the complete circle of travel. If you walk to a friend's house and back, that's a round trip. If you only walk there and someone else drives you home, that's not a round trip because you didn't return to where you started.

Scientists and engineers use the concept too. When NASA sends a spacecraft on a round trip to Mars, they plan for both the journey there and the return voyage home. The phrase round-trip time describes how long something takes to go somewhere and come back, like when you measure how long it takes for an echo to bounce off a canyon wall and return to your ears.