1. When saying goodbye, it is also necessary to distinguish between formal and informal registers:
The standard form for saying goodbye in German is "auf Wiedersehen!". It means "Until we see each other again", as does the South German and Austrian variant "auf Wiederschauen".
As you obviously can't "see" people on telephones however, you use the phrase "auf Wiederhören" - "until we hear from each other again" - when you put down the receiver.
When you are saying goodbye at night, you would say "gute Nacht!".
2. When you are saying farewell to friends and young people the above expressions can also be used. Be aware that:
The word "tschüs" (sometimes spelled "tschüss") is the most common farewell phrase amongst friends, having the sense of "See you!" or "Bye!". It originally comes, like the Spanish "adiós" and the French "adieu", from the Latin "ad deum", and means literally "God be with you".
You might occasionally find "ciao" Germanized as "tschau".
One should really only use "bis später" to meaning "See you later the same day".
The word "servus" can either mean "hello" or "goodbye" according to context. You will hear it primarily in Southern Germany and Austria.
