Feed is the distance the tool advances during one revolution of the material.
Its unit is mm/rev (millimeters per revolution). Together with cutting speed and depth of cut, it is one of the basic elements of cutting conditions.
A Closer Look
Increasing the feed removes more material per revolution and speeds up machining, but the surface becomes rougher and cutting forces increase.
Decreasing the feed produces a smoother surface but lengthens machining time.
The basic approach is therefore to use a large feed for roughing and a small feed for finishing.
Feed is a key adjustment for balancing surface quality (surface roughness) against machining time.
The optimum depends on material, tool, and required quality, so start from the tool manufacturer's recommended value and adjust.