Exactly what it says. A clay jug from the 17th Century filled with copper coinage of the era. Unfortunately Archaeologists had to be called in because metal detecting relics in Poland is illegal.
Which means - a lot of finds go undiscovered or unreported.
Link: https://www.livescience.com/17th-century-century-hoard-brimming-with-1000-coins-discovered-in-poland