What is the Italian word for hello?

Informally or colloquially: ciao!, salve!, 'giorno, 'ngiorno (G'day). The most common Word is 'ciao', pronounced like 'chow', but with an 'o' sound like the 'o' of 'point' at the end rather than a 'oo' sound: /"tSao/. 'Salve' comes from Latin and is a bit more formal than 'ciao'. You only use 'ciao' with someone you already know.

Formally: buon giorno (good morning), buon pomeriggio (good afternoon), buona sera (good evening). But on the phone is: pronto? (lit. ready?). Note you use 'pronto' only on the phone, never in person.