Kerfing is when you take your log, a nice circular saw with a sharp blade and make a run up the side of the log.
You set the blade pretty shallow at first, but every subsequent pass you drop the blade a little lower. It helps guide the split in the log. But never assume it will work to make a full deep cut on the first pass. The surface of the log is not perfectly flat and your blade will bind and burn, if not ruin the saw outright.
If you are doing chainsaw art, you will run a kerf up the backside of a log just as deep as you can get it to relieve the stresses of shrinkage as the wet wood cures. It also controls when and where the log will split so that your carving will not become damaged as it ages.
