You say 'Goodbye' to someone when you or they are leaving, or at the end of a telephone conversation.

When you say your goodbyes, you say something such as 'Goodbye' when you leave.

When you say goodbye to someone, you say something such as 'Goodbye', 'Bye', or 'See you', when you or they are leaving. You can also wave goodbye to someone.

If you say goodbye or wave goodbye to something that you want or usually have, you accept that you are not going to have it.