A kerf is a slot cut into a wood member. Typically this is done in order to use concealed plates at connections. Each connected wood part has a kerf cut into it, a continuous steel plate (a "kerf plate") is inserted in the slot, and bolted to each of the wood parts.
This effectively hides the steel plate within the wood, either for aesthetic reasons, or in order to protect the steel plate in the event of a fire. The additional work required to detail and cut the kerfs generally make this type of connection more expensive than exposed plate connections.
*Wednesday's Word Of The Week is a feature on Unalam's Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.