Direct answer: Tar pitch is the thick, heavy residue left after tar has been distilled or processed. It is darker, more solid, and less volatile than many tar oils.
Pitch can be made from wood tar, coal tar, or other tarry feedstocks. As lighter fractions are removed, the remaining heavy material becomes more viscous and pitch-like. Historical writers often used pitch and tar closely, which creates confusion.
Tar pitch has been used for waterproofing, caulking, roofing, paving, binding, and industrial carbon products. Coal-tar pitch became especially important in heavy industry but is also associated with serious occupational exposure concerns.
Tar is usually more fluid. Pitch is usually thicker, heavier, and more residue-like. The source still matters: wood-tar pitch and coal-tar pitch should not be treated as identical.
In short: A heavy residue from tar processing or distillation. Can be wood-derived, coal-derived, or otherwise tar-derived. Often used where waterproofing or binding was needed. Coal-tar pitch has recognised occupational health hazards.