You'll hear "Kalimera" all over Greece, from the staff at your hotel to people you see on the street. "Kalimera" means "Good day!" or "Good morning!" It comes from kali or kalo, meaning beautiful or good, and mera, from "imera," sometimes spelled himera, meaning "day." Just repeat it back to whoever has greeted you, and you've successfully spoken Greek.
Kalimera is especially for the morning hours, but don't worry if you blurt it out later.
No one will mind. You really do get an "A" for effort in Greece, and any attempts are welcomed and encouraged by Greeks who are touched that a person with the ill luck to have been born a non-Greek speaking foreigner is at least trying to master their own beautiful language. They will gladly help you learn as much as you like.
You may combine kalimera (or hear it combined) with "Yassas!" which is a respectful form of greeting by itself. "Yasou" is the more casual form, but if you're encountering a Greek granny, use "Yassas!" There really is not an equivalent word for "Good Afternoon" in Greek, at least not one that is used as commonly as Kalimera. Kalispera is best for the evening, but you do hear it in the later afternoon. Greece in summer also has a generous concept of afternoon—it lasts until near sundown, which can be eight o'clock or later in June. So be sure to clearly define what is meant by "I'll come by in the afternoon" if you're arranging a meeting with Greek speakers.
First of the Month Greeting
On the first day of the month, you will also sometimes hear the greeting "Kalimena" or "Kalo mena", meaning "Have a Happy Month!" or "Happy First of the Month!" That greeting probably dates from ancient times, when the first day of the month was observed as a mild holiday, somewhat like Sundays are in some places today.
More on Kalimena.
Common Tourist Mistake: Saying "Calamari" which is an Italian word for squid.
Also Known As: Greeting! Good morning, good day, hello
Alternate Spellings: Kali mera
Common Misspellings: calimera, calimara, calamari, calamara, kalemera, kalemaira, kalimara
Examples: Passing a black-garbed yia-yia on a narrow island lane? Say "Kalimera!"
Greeting your hotel keeper in the morning? That's another great opportunity to say "Kalimera."