Jointing refers to the process of filing or grinding the teeth or knives of cutting tools prior to sharpening

Sharpening

Sharpening is the process of creating or refining a sharp edge of appropriate shape on a tool or implement designed for cutting. Sharpening is done by grinding away material on the implement with an abrasive substance harder than the material of the implement, followed sometimes by processes to...

. The purpose of jointing is to ensure that all surfaces to be sharpened are of a consistent size and all imperfections have been removed.

Jointing is usually the first step in the process of sharpening:

• When sharpening a hand saw
  Hand saw
  In woodworking and carpentry, hand saws, also known as "panel saws", "fish saws", are used to cut pieces of wood into different shapes. This is usually done in order to join the pieces together and create a wooden object. They usually operate by having a series of sharp points of some substance...
  
   blade, the teeth are jointed by running a flat file
  File (tool)
  A file is a metalworking and woodworking tool used to cut fine amounts of material from a workpiece. It most commonly refers to the hand tool style, which takes the form of a steel bar with a case hardened surface and a series of sharp, parallel teeth. Most files have a narrow, pointed tang at one...
  
   over the tips of the teeth so that they are all of the same height.
• Circular saw
  Circular saw
  The circular saw is a machine using a toothed metal cutting disc or blade. The term is also loosely used for the blade itself. The blade is a tool for cutting wood or other materials and may be hand-held or table-mounted. It can also be used to make narrow slots...
  
   blades are jointed prior to sharpening so that all teeth protrude from the blade the same distance from the centre.
• Jointer
  Jointer
  A jointer is a woodworking machine used to produce a flat surface along a board's length....
  
   knives are ground until they are all the same length prior to sharpening.
• The edges of a card scraper
  Card scraper
  A card scraper is a woodworking shaping and finishing tool. It is used to manually remove small amounts of material and excels in tricky grain areas where hand planes would cause tear out. Card scrapers are most suitable for working with hardwoods, and can be used instead of sandpaper...
  
   are jointed by running the edge over a file or a sharpening stone
  Sharpening stone
  Sharpening stones, water stones or whetstones are used to grind and hone the edges of steel tools and implements. Examples of items that may be sharpened with a sharpening stone include scissors, scythes, knives, razors and tools such as chisels, hand scrapers and plane blades...
  
  prior to turning the burr.

Jointing is usually carried out infrequently as it removes a lot of material from the edge of the blade.