GSC

From Memory Alpha, the free Star Trek reference.

GSC is a unit of measure describing pressure in grams per square centimeter.

[edit] Comparative measurements of pressure

• A Klingon Raptor-class warship is capable of withstanding atmospheric pressure of 15,000 GSC, or that found in a Class 9 gas giant approximately 2 kilometers in its atmosphere. That pressure is also well within the tolerance of a 22nd century Earth Starfleet shuttlepod. (ENT: "Sleeping Dogs")

• Apollo's hand was capable of creating over 1,000 GSC of external pressure on the hull of the USS Enterprise. Above 1,000 GSC, and the systems aboard a Constitution-class start to become critical. (TOS: "Who Mourns for Adonais?")

• Defiant-class starship are capable of withstanding a hull pressure exceeding 9,000,000 GSC. (DS9: "Starship Down")