From Halopedia, the Halo wiki
Gekz is a currency used by the Covenant client species during its reign. After the fall of the Covenant Great Schism in 2552 it saw continued use despite the lack of the Covenants treasury checks and minutely detailed systems.
When Sav Fel stole Pious Inquisitor, Avu Med 'Telcam put out a reward of 80,000 gekz for the return of the ship, which the Skirmisher Chol Von accepted. A fifty-gekz chip was enough for Chol Von to bribe an Unggoy caretaker on the Station of Constant Sustenance.[Note 1]
List of appearances