a resinous liquid obtained as a byproduct in the manufacture of chemical wood pulp: it is used in the manufacture of soap, varnishes, linoleum, etc.
See tall oil in American Heritage Dictionary 4
(täl, tôl)
noun
A resinous oily liquid composed of a mixture of rosin acids and fatty acids obtained as a byproduct in the treatment of pine pulp and used in soaps, emulsions, and lubricants.