@yankee7548, kerf is the amount of material removed by the width of the tool used to cut, be it be a saw, a rotary tool like a cnc or a laser beam. It is important if you intend to fit pieces together with each other in a construct.
Here is one explanation in the forum
https://community.glowforge.com/t/to-adjust-for-kerf-or-not-to/2619
but this topic has been discussed amply and if you search you will find more valuable information.