What is 'Jackknifing' (Efecto Tijera) in an articulated tractor-semitrailer combination, and what is its primary trigger?

1. An intentional parking maneuver used in tight loading docks
2. A catastrophic loss of directional stability where the tractor drive wheels lock up on a slippery surface, causing the semitrailer to push the rear of the tractor sideways until the cab and trailer fold into a V-shape
3. The automatic uncoupling of the kingpin at highway speed
4. An electrical short circuit in the trailer tail lights