Góðan daginn (“Good day”) is a very common greeting, used from early morning until 6PM (that’s when the day turns into an evening). You use it:
  • To say “good morning” to your family members when you wake up.
  • To greet strangers you meet on the street.
  • To greet waiters, bartenders, and other staff.
  • To greet your customers.
Notice that the phrase is using the accusative case (the second case) rather than the nominative case (the first case) as one would assume. It makes sense if you think of the phrase as being a shortened version of “(I hope you have) a good day”.