"Oi" is a casual greeting commonly used in British English, particularly in informal settings. It is often used to get someone's attention or to express surprise. The term can convey friendliness or annoyance, depending on the context and tone. The word has its roots in the Cockney dialect of London and has spread to various English-speaking regions. While it is widely recognized, it may not be appropriate in formal situations. Overall, "Oi" reflects the informal and playful nature of everyday conversation.