Grind size means the size of your coffee grind, grind size is divided into 3 groups Fine which means fine grind
Medium: is a grind that is not too fine but not too coarse either Coarse: is a type of grind that is quite coarse with a range

The finer the grind size that is ground, the longer the extraction time created in the coffee machine. Because the flow of water that falls is increasingly held back by the coffee powder itself, so the longer the water phase touches the coffee which creates a more intense flavor.

Generally making coffee with espresso shots will use a fine grind, while coarse grinds are usually used in manual brew techniques or post-roasting cupping processes.