Resurfacing is a process that removes the track from the ball.
This is done generally by sanding but if machines are used diamond cutters can be employed. The ball is made slightly smaller in the process, how much smaller depends on how deep the track is. You don’t generally try to remove any deep gouge mark just the track.
A ball with a well established track is flatter in that area. This can cause the ball to loose some ability to carry. Resurfacing rounds the track area and smoothes the surface. It also removes a small layer of oil soaked cover stock.
Most resin balls can use a resurfacing after 200 to 300 games.
I have resurfaced balls up to 6 times with good success.