"Gluckauf!” also written "Gluck Auf!", is the German miner's greeting. Literally this can be translated with "Luck up" or "Luck open", but this is meaningless in English, so a better translation would be "Good luck". Its original meaning was lost during the centuries, but the most reasonable explanation is that it means "the ore veins shall open for the miner". Another explanation is described in the section “Holy Barbara". Yet, a translation does not carry the meaning of "Gluckauf". For a German miner, greeting somebody with this word means that you belong to and care for each other, and that you belong to the same family: the family of all miners in the world.
It is not clear where this greeting originated, but it has been used since the 16th century. The oldest written proof dates back to 1575 when Hans Zobeld named one of his mines in the Erzgebirge (Ore Mountains) "uffm Gluck auff'. In the 17th century, "Gluck auf!" was already the common miner's greeting in the Erzgebirge. Through history, the word was exported to all countries that once were a part of Germany, and today you will find similar expressions in the Czech Republic, Austria, Poland, or Slovenia.
I guess even most of the younger miners don't know about this, we use it in the office as well.
I didn't know myself until about 3 years ago, to be honest.