Ciao Samantha, Usually in formal situations we use "arrivederci" to say goodbye. Between friends we tend to say "ciao" or "ciao ciao" with the same meaning. Ciao is also use to say "hello". Addio is used for a farewell.

ohh!! thank you so much for the info!!

"Addio" is very rare. It means you won't see that person ever again, or at least for a very long period of time. Ciao = informal greeting and farewell Salve = "medium formality" greeting Arrivederci = formal farewell