A round trip is something that travels from one location to another, and then back again. A common abbreviation for a round trip in the travel industry is R/T. The standard opposite of a round trip is one-way.
Round trip often refers to transportation, where travel is booked from Point A to Point B and then from Point B to Point A, often called a round-trip ticket.
Round trip is usually the preferred spelling for the noun, while the hyphenated “round-trip” is often preferred as a modifier. However, along with the single-word “roundtrip,” these spelling variations are often used interchangeably. A round trip may also be called a return; a round-trip ticket may be called a return ticket.