What is the meaning of Jack-knife?

A compact folding knife.

The front-dive pike, in which the body folds and unfolds.

A semi-trailer truck accident in which the vehicle mimics the closing of a jack-knife.

A game of skill played with a pocket knife in which participants try to throw or flip the knife to stick upright in the ground at specified points or areas; mumblety-peg.

Alternative spelling of jackknife.

To fold in the middle, as a jackknife does.

To cause a semi-trailer truck to fold like a jackknife in a traffic accident.

Source: wiktionary.org