Formal:
* Bom dia: Good morning (used until noon)
* Boa tarde: Good afternoon (used from noon to evening)
* Boa noite: Good evening (used from evening onward)
Informal:
* Oi: This is the most common and versatile greeting, suitable for friends, family, and acquaintances.
* E aí: This is a casual greeting, similar to "What's up?"
* Olá: This is a more formal "hi" than "oi," but still informal.
Other options:
* Tudo bem? (How are you?) This is a common way to greet someone, and it's usually followed by a response of "Tudo bem."
* Tudo bom? (Is everything good?) This is similar to "Tudo bem?" but slightly more informal.
Important note: In Brazil, it's common to shake hands or give a quick hug when greeting someone you know, even if it's just a casual encounter.
Ultimately, the best way to say "hi" in Brazil is to observe how others greet each other in the situation.