A Fals is a monetary unit used in the Middle East such as in Jerusalem. 4 fulus equal to 1 Dirham, and therefore 16 fulus equal to 1 Dinar.
It is roughly equivalent to the Copper coins of the Summer Lands. Arthur had some fulus in his Purse from Mohammed.
Behind the scenes[]
The fals (فَلْس) was an historical coin. The Arabic plural form is properly "fulus" (فُلُوس) but this is never used in the game.