You know how it goes; you see someone in the morning, you say ‘good morning’. The same applies in German. You can say Guten Morgen. But after that… at some point in the later morning, people switch from saying Guten Morgen and instead say Mahlzeit. That means, literally translated. Meal time. Mahlzeit is what you say when you are about to start eating a meal, kind of like the French bon apetite. But strangely enough, it is also used as a greeting. If you pass someone in the corridor at work and they are carrying food, chewing something, or hell, even look like they might be heading to the canteen, you say Mahlzeit to them, instead of hello.
It’s hard to get used to, but I’m getting there.