interjection
Casual farewell, often used with children or in informal settings. Equivalent to English 'bye-bye'.
バイバイ、また明日ね。
Bye-bye, see you tomorrow.
noun, noun or participle which takes 'suru', intransitive verb
Noun and suru-verb use for the act of saying goodbye. Common in phrases like バイバイする.
子供は先生にバイバイした。
The child said bye-bye to the teacher.