Bye/baɪ/ Definition 1 of 3Pro Tip 1/3Informal Farewell Use 'bye' in casual conversations with friends, family, or peers. See you tomorrow, bye! Pro Tip 2/3Quick Exit 'Bye' is suitable when leaving abruptly or in a hurry. Oops, I'm late, bye! Pro Tip 3/3Expressing Endearment Saying 'bye bye' can sound affectionate, often used with children. Goodnight little one, bye bye!