"Oi!" is a casual greeting commonly used in British English and Australian English. It is often employed to get someone's attention or to express surprise. The term can convey friendliness or informality, making it popular in everyday conversations among friends and acquaintances. In addition to its use as a greeting, "Oi!" can also serve as an interjection to express annoyance or to call out to someone. Its versatility makes it a staple in various social contexts, reflecting the relaxed nature of informal communication in English-speaking cultures.