Stargate forcefield deactivation code
From The Stargate Omnipedia
Code used to deactivate the energy forcefield surrounding a Stargate that is protected by such a device. One such code was sent to the Alpha Site, and later used by teams from the S.G.C. to access the planet Erebus by deactivating its Stargate forcefield. Bra'tac had transmitted the code several months prior when he realized he had been captured on the planet, knowing that the S.G.C. base at the Alpha Site would record it.
KEY EPISODE
Orpheus - Jackson discerns the forcefield deactivation code to allow S.G. units to emerge on Erebus unharmed.