Jack Tar was the common Englishman's affectionate name for the sailors of the Royal Navy during the time of the British Empire. There are two plausible etymologies for this name. Sailors frequently wore coats and hats made from a waterproof fabric called tarpaulin. This may have been shortened to "tar" at some point.

Also, in the age of wooden sailing vessels, a ship's rigging was rope made of hemp, which would rot quickly in such a damp environment. To avoid this, the ropes and cables were soaked in tar. Since it was a routine part of a sailor's day to "clap on to" and "heave" these ropes, his hands would be stained with tar, and thus earned the nickname "tar".