Direct answer: Tar resin is an ambiguous phrase that usually refers to resinous material within tar, tar blended with resin, or a tar-like resin product. It is not a precise standard term.
The confusion comes from conifer materials. Pine trees produce resin, resin can yield rosin and turpentine, and resin-rich wood can yield pine tar. In old craft language, tar, resin, rosin, pitch, and gum are often discussed together.
Tar resin may appear in craft recipes, varnishes, boat coatings, old trade catalogues, or translated technical writing. The reader should check whether the writer means pine resin, rosin, tar, pitch, or a mixture.
Resin is a plant exudate or resinous substance. Tar is normally produced by heating organic material. Rosin is a solid residue from processing resin. Pitch may be a heavy tar or resin-derived material. Tar resin sits in the messy overlap of these terms.
In short: An ambiguous term rather than a fixed material. Often connected with pine, resin, rosin, pitch, and tar mixtures. Needs context before use or identification. A good internal link hub for resin versus tar explanations.