Enjoy the beer that you deserve.
A stein is a mug made of clay or ceramic. They often have a hinged lid, usually made of pewter, with a convenient thumb lever near the handle for opening and closing.
Typical volumes range from 16.9 to 101 ounces (0.5 to 3.0 liters)!
In addition to looking good, the lid serves the extremely welcome and practical purpose of keeping unpleasant items, like flies, out of the beer.
Stein is German for "stone", and is probably short for steinkrug (“stone jug”). They are a colorful and functional symbol of German beer styles.