A ticket valid for travel in one direction only (a one-way ticket), as opposed to a round-trip ticket.
東京行きの片道切符を買いました。
I bought a one-way ticket to Tokyo.
留学するので片道切符で行くつもりだ。
I'm going to study abroad, so I plan to go with a one-way ticket.
自動券売機で片道切符を購入できます。
You can buy a one-way ticket at the ticket machine.