One-way ticket

One-way travel is travel paid for by a fare purchased for a seat on an aircraft, a train, a bus, or some other mode of travel without a return trip. One way tickets may be purchased for a variety of reasons, such as if one is planning to permanently relocate to the destination, is uncertain of one’s return plans, has alternate arrangements for the return, or if the traveler is planning to return, but there is no need to pay the fare in advance.

In the case of a passenger that wants to stay at the destination for more than 365 days (12 months) then a one-way ticket is advised by airlines and travel agents (as normal return tickets are valid for 12 months or 365 days).

One way tickets are more expensive (especially when the origin of travel is from one zone to another zone[clarification needed]) but if within the same zone then it can be half of the return ticket price.

Following the September 11 attacks, one-way tickets into the United States when purchased for air travel drew suspicion because the hijackers involved in the attacks had one-way tickets.

Source from Wikipedia