The narg was a unit of currency used by Androgums in the Third Zone.
According to Shockeye of the Quawncing Grig, a twenty-narg note could be changed "anywhere in the nine planets." Despite this, Oscar Botcherby, a restaurant manager in 20th century Spain, refused to accept the currency. (TV: The Two Doctors)
The Seventh Doctor carried a twenty-narg note, amoung the various currencies in his pockets. (PROSE: First Frontier)