The Pratt knot, also known as the Shelby or Pratt-Shelby, is a way of tying a necktie. It produces a medium thickness knot that is symetric and uses very little length.
Why you want it- The Pratt knot is ideal for a shorter necktie because it uses very little length. The because it is medium thickness and symetric, it works on most types of collars and is a great intro to the Windsor knot. For how to tie it, see above.