The process of cutting or forming threads using a tap is called “tapping”, whereas the process using a die is called “threading”.
Taps and dies are tools used to create screw threads, which is called “threading”. A tap is used to cut or form the female portion of the mating pair (e.g., a nut). A die is used to cut or form the male portion of the mating pair (e.g., a bolt).
Both tools can be used to clean up a thread, and this is referred to as “chasing”. However, using an ordinary tap or die to clean threads will generally result in the removal of some material, which will result in looser and weaker threads. Because of this, threads are typically cleaned using special taps and dies made for this purpose, which are known as chasers. Chasers are made of softer materials and are not capable of cutting new threads, however they are still tighter fitting than actual fasteners and are fluted like regular taps and dies (to provide a means for debris like dirt and rust to escape). One particularly common use is for automotive spark plug threads, which often suffer from corrosion and a build-up of carbon.