Formal:
Buongiorno: This is the most formal way to greet someone and is appropriate for any time of day. It literally translates to "good morning" but is used throughout the day in formal contexts.
Informal:
Ciao: This is the most common and versatile way to say hello in Italian, used among friends, family, and even acquaintances. It can be used at any time of day.
Salve: This is a more polite and formal greeting than "ciao" but still less formal than "Buongiorno." It's suitable for situations like greeting someone you don't know well or in professional settings with colleagues.
Here are some additional greetings you might encounter:
Buona sera: Good evening (used after sunset)
Buona notte: Good night
Buongiorno/Ciao a tutti: Hello everyone (plural)
Remember, when greeting someone formally, it is customary to shake hands and make eye contact.