Grinding dresser

A grinding dresser or wheel dresser is a tool to dress (that is, slightly trim) the surface of a grinding wheel. Grinding dressers are used to return a wheel to its original round shape (that is, to true it up), to expose fresh grains for renewed cutting action (including cleaning away clogged areas), or to make a different profile (cross-sectional shape) on the wheel's edge.

The objective of dressing the wheel is to:

Also an abrasive wheel type that has a small "grinding wheel" in a holder that is held against the spinning grinding wheel to dress and clean the face of the grinding wheel.

Four types of dressers are used to dress the wheels of CNC grinders used for grinding complex shapes. This type of dresser is mainly in use on CNC grinding machine tools to automatically dress the grinding wheel via computer control in specialist areas requiring complex shapes such as grinding bearing raceways.

...
Wikipedia