Direct answer: Boat tar is a practical name for tar used on boats, especially traditional pine tar used to protect wooden parts, rope, and maritime fittings.
Before modern coatings, wooden boats relied on materials that could move with timber, resist water, and be renewed. Pine tar and related mixtures were part of this maintenance culture. Their value came from repeatable care rather than permanent one-time protection.
Boat tar appears in traditional boatyards, Scandinavian wooden-boat maintenance, restoration discussions, and maritime heritage. It may be used on exposed wood, ropes, spars, or fittings when appropriate for the vessel and product.
Boat tar does not identify one recipe. Some products are straight pine tar. Others are mixtures with oil, turpentine, or pigments. Historic recipes varied by yard and job.
In short: A practical use name, not a single material formula. Usually points toward pine tar in traditional wooden-boat contexts. Used for maintenance and protection of natural materials. Modern products and historic recipes vary.