Direct answer: Tar lacquer is a dark lacquer-like coating that uses tar, bitumen, pitch, or tar-derived ingredients to create a protective or decorative black finish.
The phrase appears where lacquer is used broadly for a hard, glossy, protective finish. In some industries, black bituminous or tarry coatings were called lacquers because they formed a dark film on metal, wood, or other surfaces.
Tar lacquer may be found in old coating catalogues, industrial finishes, decorative blackwork, waterproofing, and restoration contexts. It is a terminology article more than a modern shopping category.
Traditional East Asian lacquer, shellac varnish, bituminous lacquer, and tar lacquer are different things. The word lacquer describes finish behaviour and appearance more than one ingredient.
In short: A dark coating phrase with variable ingredients. May involve tar, pitch, bitumen, or related black materials. Often describes appearance and function rather than exact chemistry. Needs context from the trade or period.