Okay, the word 'Tschüß' (or 'Tschuess' if the characters won't be shown correctly) has many different appearances. The base form is 'Tschüß' (Tschuess). In some parts of Germany you will hear 'Tschau'. Here in Frankfurt we say 'Atschö' (Atschoe) which let you feel the origin source of language - French!
It is the well known word 'adieu' or also known as 'adios' (in spain) and 'ciao' (in italy).

I think it is the most used greeting word all over the world after Hallo, Hello, Hola...

Another thing is your salutation to me because 'Achtung' means 'attention' and I don't like to be in school here...

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Greetings from Frankfurt (Germany),
Sheriff ;-)