It is a wrong attempt to define a concept whose meaning and purpose are already embedded in the word. Therefore, let's formulate how the coffee grinder works. The purpose of grinding the beans is to ensure that the surface area of the beans is optimal for proper extraction (removal of flavors from the coffee). The optimal particle size of the grain is different for each coffee making method, so the types of coffee grinders we will focus on are different. Coffee grinders are blades and burrs.
Knife - the simplest inexpensive mechanical devices equipped with a motor, on which a mechanical blade, such as a sickle, is attached. Close the lid of the chamber where you put the roasted beans and press the button. The blades at the bottom of the bowl will break the bean into pieces. The only advantage of this method is speed and affordable price. And the shortcomings are quite serious. The grinding value here is not regulated in any way and cannot be controlled - the device pulverizes the grain. And there may still be large particles. Therefore, it will not be possible to prepare a delicious cup of coffee from this grain. Small particles threaten the drink with dustiness, viscosity, bitterness (bitter / sour depending on the coffee), and large particles - juiciness, rancidity.
The burr grinders are equipped with cutting discs with adjustable distance between them. By changing this, the grinding value changes. The coffee particles do not leave the chamber as much as the distance between the millstones. This provides greater homogeneity in grinding. Such coffee grinders are manual and electric, and the grinding stones inside are steel and ceramic.
Burr grinders are also divided by purpose: for #espresso and filter methods. After all, it takes a very fine grind to make espresso, and there are many variations of medium to coarse filter methods.