A knife is a sharp-edged (single or double edged) instrument consisting of a thin blade used for cutting and fitted with a handle. The knife can be used as a tool or a weapon. Considered by some to be one of the most useful tools of all time, its origins date as far back as two-and-a-half million years ago, as evidenced by the Olduwan tools.

History
Today, knives come in many forms but can be categorized between two different types: fixed blade knives and folding, or pocket, knives. Although each has inherent advantages, the two have many similar characteristics.
Modern knives consist of a blade (1) and handle (2). The blade can be fine or serrated. The handle, used to grip and manipulate the blade safely, may include the tang, a portion of the blade that extends into the handle. The blade consists of the point (3), the end of the knife used for piercing, the edge (4), the cutting surface of the knife extending from the point to the heel, the grind (5), the cross-section shape of the blade, the spine, (6), the top, thicker portion of the blade, the fuller (7), the groove added to lighten the blade, and the bolster (8), the thick portion of the blade joining the blade and the handle. The guard (9) is a barrier between the blade and the handle which protects the hand from an opponent, or the blade of the knife itself. A choil, where the blade is unsharpened and possibly indented as it meets the handle, may be used to prevent scratches to the handle when sharpening or as a forward-finger grip. The end of the handle, or butt (10), may allow a lanyard (11), used to secure the knife to the wrist.

Materials and construction

Main article: Blade Blade
A fixed blade knife does not fold or slide, and is typically stronger due to the tang, the extension of the blade into the handle, and lack of movable parts.

Fixed blade features
A folding knife can pivot, allowing the blade to fold into the handle. Although not likely to have a guard or full tang, folding knives typically have a locking mechanism. One common mechanism, found traditionally on pocket knives, is the slip joint. Once opened, the blade does not lock, but is held in place by a spring device that allows the blade to fold if a certain amount of pressure is applied. Alternately, the lockback can be used. Like the slip-joint the lockback includes a pivoted latch connected to a spring, and can be disengaged only by pressing the latch down to release the blade.
Another feature associated with the folding knife is a small knob, disk or hole that allows the user to open the knife with one hand, leaving the other hand free.

Folding blade features
A sliding knife is a knife which can be opened by sliding the knife blade out the front of the handle. One method of opening is where the blade exits out the front of the handle point-first and then is locked into place (an example of the this is the gravity knife). Another form is a O-T-F (out-the-front) switchblade, which only requires the push of a button or spring, the knife is "slid" out of the handle, and locked into place. To retract the blade back into the handle, a release lever or button, or linerlock is pressed.

Sliding blade features

Main article: Handle (grip) Handle

For more details on the various types of knives, see Blade#Patterns of knife blades. Knives as weapons
A primary aspect of the knife as a tool includes dining, used either in food preparation or as cutlery. Examples of this include:

Bread knife: A knife with a serrated blade for cutting bread
Boning knife: A knife used for removing the bones of poultry, meat, and fish
Carving knife: A knife for carving large cooked meats such as poultry, roasts, hams
Chef's knife: Also known as a French knife, a cutting tool used in preparing food
Electric knife: An electrical device consisting of two serrated blades that are clipped together, providing a sawing action when powered on
Kitchen knife: Any knife, including the chef's knife, that is intended to be used in food preparation
Table knife: A piece of cutlery, either a butter knife, steak knife, or both, that is part of a table setting, accompanying the fork and spoon Knives as utensils
As a utility tool the knife can take many forms, including:

Bowie knife: Commonly, any large sheath knife, or a specific style of knife designed by Colonel Jim Bowie
Butterfly knife: A folding knife also known as a balisong, with two handles counter-rotating around the tang such that, when closed, the blade is concealed within the handles
Diver's knife: A knife adapted for use in diving and watersports and a necessary part of standard diving dress
Electrician's knife: An insulated knife used to cut electrical wire
Hunting knife: A knife used to dress large game
Pocket knife: Also known as a multi-tool or jackknife, a knife which may contain several blades, as well as other tools
Palette knife: A knife, or frosting spatula, lacking a cutting edge, used by artists for tasks such as mixing and applying paint, and in cooking for spreading icing
Scalpel: A medical knife, used to perform surgery
Straight razor: A reusable knife blade used for shaving hair
Survival knife: A sturdy knife, sometimes with a hollow handle filled with survival equipment
Switchblade: A knife with a folding blade that springs out of the grip when a button or lever on the grip is pressed
Utility knife: A knife used for cutting sheet materials, including cardboard boxes
Wood carving knife: Knifes used for wood carving, often with short and thin blades for better control Knives as tools

Kukri: A Nepalese knife used as both tool and weapon
Laguiole knife: A traditional French pocket-knife, originally produced in the town of Laguiole in the Aveyron region of southern France in the early 19th century
Lajinaa: A small spear, sometimes used in close range battles, used mostly by Spaniard pirates who raided trade ships in the gulf coast
Mora knife: Similar in design to Finnish puukkos, a range of belt-knives manufactured by the cutleries of the town of Mora in Dalarna, Sweden
Opinel knife: A simple, inexpensive, wooden pocket-knife, manufactured since the 1890s in the town of Saint-Jean-de-Maurienne in the Savoie region of France
Puukko: A traditional Finnish or Scandinavian style woodcraft belt-knife used as a tool rather than a weapon
Sabatier: A cooking knife manufactured in Thiers, France from well established manufacturers from the early 19th century
Seax: A Germanic single-edged knife, used primarily as a tool, but may also have been a weapon
Swiss Knife: A multiple-purpose pocket Swiss tool (see Pocket Knife above), usually containing several blades of different lengths, a corkscrew, a can-opener, a toothpick, tongs and even a little wood-saw and scissors sometimes. It was created in 1891 for the Swiss military.
Ulu: An Inuit woman's all-purpose knife Knives as a tradition
See also: Ritual and Superstition
The knife plays a significant role in some cultures through ritual and superstition. As the knife was an essential tool for survival since early man

Rituals and superstitions

Main article: Knife Legislation Further reading