A farewell interjection meaning 'goodbye' or 'farewell' (often a shortened form of さようなら).
友達に『さよなら』と言って駅を出た。
I said 'goodbye' to my friend and left the station.
パーティーの最後にみんなでさよならを言った。
At the end of the party everyone said goodbye.
電話でさよならを告げた。
I said goodbye over the phone.
The act of saying goodbye or putting an end to something (noun/verb usage), e.g., saying goodbye to bachelor life.
彼は独身生活にさよならした。
He said goodbye to his bachelor days.
古い習慣にさよならを告げる時が来た。
The time has come to say goodbye to old customs.
そのプロジェクトはさよならを迎えた。
That project has come to an end.
Used for a farewell performance/event or the final/decisive instance (e.g., a 'farewell game' or 'farewell concert').
彼のさよなら試合で、彼は感動的なホームランを打った。
In his farewell game he hit an emotional home run.
明日はバンドのさよなら公演だ。
Tomorrow is the band's farewell concert.