It's 5:00 PM in Italy, you walk into a gift shop, and say "Buongiorno." The sales clerk responds with: "Buonasera." You're confused. You think to yourself: "Why didn't she say 'boungiorno?'
The best answer is Italians have different greetings at different times throughout the day. Here are the basic greetings you can use in Italy for the morning, evening, and late night.
Mornings and Daytime - Buongiorno
You hear this the most. Buongiorno literally means "good day."
Buona giornata - "Have a good day" You can say this when you leave a place.
Ciao -hello and goodbye between friends/family. Use it if you know them. A good tip is to use "ciao" only after the Italian says it to you. Smile for you can consider yourself a friend of theirs. Most likely if you have had a good experience with an Italian, you were kind and considerate, they will use the term with you when you leave.
Ciao Cara - "hello dear"
Ciao Amici - "hello friends"
After 4:00 PM - Buona Sera
Buonasera is reserved for around/after 4:00 PM. It means "good evening." You may even hear it before then depending on the Italian. A good tip is just to repeat the greeting they offer you. If they greet me with "Buonasera," then I say back "Buonasera."
Buonaserata - "Have a good night" - You can say this when you leave a place or person after 4:00 PM.
Late Night - Buona Notte
Buona Notte means "good night." This phrase is used only when you see them for the last time that evening. Like when you are going to bed or leaving a restaurant after a late dinner.
I hope this clears up some confusion you may have when you hear Italian greetings.
My best advice even when you are in doubt, keep greeting Italians. It is the best gesture you can make for establishing a good rapport with your local community. Italians respect guests that make an effort.
If you want to know a few more Italian words and phrases for your time in Italy you can read my blog post HERE