The Farthing (F) is a copper coin. It is the smallest unit of payment in Drakensang.
1 gold Ducat (1D) = 10 silver Thalers (10T) = 100 copper Farthings (100F)
In the world of TDE, the Farthing can be subdivided further into Kreutzers (1 Farthing = 10 Kreutzers), but that unit is not implemented in Drakensang.
Aventurian money also has weight; ten Farthings weigh one ounce. However, in Drakensang money is stored in the Quest Bag and therefore in effect "has no weight".