Hi 53,
The mechanical advance is a device in many distributors under the breaker plate that allows the rotor to advance timing through centrifigal weights and draw back springs. The tension on the springs control how fast you get mechanical advance. On GM V8 engines the mechanical advance is on top of the distributor, the two things that pivit out and springs pull back and holes drilled for the rotor screws. Its not slang as per say, but what the device actually does.
Truck Tinker
