Direct answer: Naval tar is the tar used in wooden shipbuilding and maintenance, especially pine tar and related naval stores used on rigging, seams, and timber.
The phrase belongs to the age of wooden ships. Navies and merchant fleets needed dependable materials to waterproof, preserve, lubricate, seal, and maintain vessels. Tar, pitch, rosin, and turpentine became known as naval stores because they were vital supplies for shipyards and seafaring nations.
Naval tar was used on ropes, standing rigging, wooden surfaces, seams, and other exposed parts of ships. It helped natural fibres and timber resist water, salt, and decay. Its smell became part of maritime culture, and “tar” even became a nickname for sailors in some English usage.
Naval tar is a use category rather than a separate chemical species. In most historical wooden-ship contexts it points toward pine tar or other wood tar, often worked together with pitch and related resin products.
In short: A historical use category tied to wooden ships. Often involved pine tar, pitch, rosin, and turpentine. Important for rigging, timber, and waterproofing. Part of the wider naval stores industry.