Mahlzeit is a German salutation, which is used during lunchtime. It descended from a more formal salutation and is the short form of "Gesegnete Mahlzeit" (archaic term, de: blessed meal). Mahl is the German word for meal. Mahlzeit is the German word for meal time.
The salutation is uncommonly used without connection to food or eating. In most German regions and in Austria it still has its old meaning and is only used in connection with meals.
When saluted with Mahlzeit one just answers Mahlzeit. 
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