Even if you don’t know Italian, certainly you are familiar with the phrase “Ciao!” (pronounced: chou) which is used as an informal greeting or way of saying goodbye. Typically we use ciao when saying hello or goodbye to our friends or greeting people that you are acquaintances with.
Typically you do not use “ciao,” when you are greeting people you do not know… for example at the bank or in stores, it is more polite to say
Buongiorno (good day) – use this in the morning or anytime before 3 or 4 PM.
Buonasera (good afternoon/goodevening) – used in the afternoon, and always after sunset.
I have also heard people use the term: “Salve,” which means “hello,” however is more formal than ciao.
When answering the phone, most Italians say “Pronto,” (go ahead) or “Si” (which means yes).
However, back to the word Ciao!
I recently discovered that this term was used during the Middle Ages. During the middle ages, it was common to greet someone by saying “Sono vostro schiavo,” which was shortened to “ciau.” (“Ciau,” is from the Ventetian dialect – coming from Venice. It is important to remember that different dialects are spoken in different areas of Italy. Some of them are so different from Italian that it is impossible to understand what exactly is being said if you are not familiar with that dialect.)
“Ciao first appears in English in 1929 in Hemingway’s A Farewell to Arms, which is set in northeast Italy during World War I.” (http://www.thefreedictionary.com/ciao)