Direct answer: Tar grease is a practical mixture of tar with greasy, oily, or fatty materials, historically used where a sticky protective lubricant or dressing was useful.
Old working materials were often blended on site. Tar could be mixed with fat, oil, tallow, resin, or other ingredients to make it spread differently, cling to fibres, or stay flexible. The phrase tar grease can therefore mean a mixture rather than a manufactured standard.
Tar grease may appear in rope work, farm equipment, axles, outdoor ironwork, leather, or old maintenance writing. In naval stores history, tar also had land uses such as axle grease and fencepost protection.
Plain tar, tar oil, and tar grease behave differently. Grease suggests a softer, lubricating, smearable mixture. The exact performance depends on the added oil or fat.
In short: A tar-based mixture rather than a single chemical material. Historically associated with lubrication, dressing, and protection. May include fats, oils, or resins. Exact meaning depends on the old recipe or trade context.