A monetary unit. Like the "Dollar". Originally it was a "Gulden Florijn", (golden florin) named after the Italian "Fiorino d'Oro". Earliest mention is in the mid 1300's. In the early 1800's it went decimal, ie 1 Gulden is 100 Centen. Over time it was shortened to "Gulden" until 2002 when The Netherlands adopted the Euro.