What does it mean when says pass key on your 99 Chevy venture van?

On a 1999 Chevy Venture, a "pass key" refers to the ignition key system that's linked to the vehicle's security system. It's designed to prevent the vehicle from being started with an incorrect key. The key itself has a chip embedded in the head that communicates with the car's computer. If the chip doesn't match the car's system, the vehicle won't start, even if the key's physical teeth turn the ignition cylinder.