Langley was an American city in the state of Virginia. As the Central Intelligence Agency's headquarters were located in Langley, "Langley" was a common metonym to refer to the CIA.
During Day 1, when Richard Walsh ordered all section heads to CTU shortly after midnight, Tony Almeida tried to call Langley as well as the bureau to find out what was going on. However, nobody knew anything about the order, so Tony passed this on to Nina Myers. ("Day 1: 12:00am-1:00am")
Findings at CTU · Operation Hell Gate · Veto Power · Trojan Horse · Cat's Claw · Vanishing Point · Chaos Theory · Storm Force · Collateral Damage · Trinity · Head Shot · Death Angel · Deadline · Rogue · Trial by Fire