What does 'jackknifing' refer to in driving?

Jackknifing refers to a situation in which a combination vehicle, such as a tractor-trailer, experiences a critical angle between the tractor unit and the trailer. This occurs when the trailer swings out to the side, causing the two parts to fold towards each other, resembling the position of a folded knife. Typically, this can happen during hard braking or on slippery surfaces, where the rear wheels of the tractor lose grip, allowing the trailer to push sideways relative to the tractor. Recognizing the signs of potential jackknifing is essential for drivers, as it can lead to loss of control and serious accidents. Understanding this phenomenon can help drivers take preventive measures, such as maintaining safe distances and adjusting their speed to road conditions.