In Germany, beer steins are called "krug" or "steinkrug"

[steve2470]

What we, in the English speaking world, call “beer steins” aren’t called such in Germany (the country with which the heavy hinge-lidded earthenware drinking mugs are most closely associated). In Germany, they are called “krug” or “steinkrug” and the usage in English is believed to have originated from the truncation of the German word for stoneware, “steinzeug”.

-from today's howtogeek.com newsletter

[FSogol]

1. Know why they have lids?

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To keep the flies out.

[dchill]

2. Or, possibly, in.

[jmowreader]

3. They are also called "obsolet."

In Berlin at least, and I assume in the rest of Germany, every establishment that sells beverages must have this kind of glass washing device:



Lidded steins won't fit in this.