A jackknife is a knife that has a mechanism that allows the blade to fold inward when not in use. It was invented in 1711 by Jacque de Liege as a way to safely carry a knife so that the blade was covered until needed. The jackknife is also known as a pocket knife as many men would carry the knife in a pocket and use it to whittle, or carve, sticks and pieces of wood.
The jackknife is a handy camping tool, especially in backpacking as it doesn't take up much room or weigh a lot. The knife can be used to sharpen the ends of sticks to use to roast hot dogs or marshmallows over a fire. It can also be used to carve wooden eating utensils such as chopsticks or tools to stir food in cooking pots. Expert jackknife users can carve a series of notched wooden sticks to fit together to form racks for holding cooking pots over a fire or make a fish cooker out of both straight and curved sticks.
Jackknives can also be used to create wooden fishing lures, letter openers, pot hooks and whistles. Some wood carvers even make toy boats out of a piece of cedar with a jackknife. Wooden bowls can also be carved with a jackknife, and of course practically any type of sculpture is possible with the right piece of wood.
The jackknife's inventor, French knife maker Jacque de Liege, created a back-spring assembly to allow the knife to fold. The term jackknife evolved in English to refer to many other things that fold inwards. For example, a type of dive in which the body is tucked inward is called a jackknife and a trailer truck that folds inward in an accident is said to have jackknifed.
The jackknife is also sometimes called a scout knife and is associated with scouts using the knife on scouting trips. The Swiss Army Knife is a brand of jack knife that features many fold-out tools on it besides just a blade. Premium jacks, or premium jackknives, are narrower than regular jacks, or regular jackknives.