A commemorative coin, struck, as the name indicated, for a jubilee, anniversary, etc. They are also known as Denkmunzen or Gedachtnismunzen.
There are a number issued on the centennials of the Augsburg Confession, 1530, 1630, 1730, and 1830; and in 1755 Frederick III, Duke of Saxe-Gotha, struck a Thaler on the peace of the religions. See Madai, Vollstandiges Thaler-Cabinet. 1765-74 (4013). In Holland similar pieces have been issued known as Gedenkpennige.
See Also: Jubileums Thaler
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)