We’re not aware of definitive interpretations of these terms in modern parlance (say, Newtonian physics in the case of jin or biomedical science in the case of qi). Master Liu does an excellent job in explaining these terms correctly in the context of tai chi (see his introductory article), true to his Wu (Hao) lineage (see FAQ #7 below). From his experience of practicing TCM tui na, working with the tendons of the body, Master Liu also has some interesting explanations of the mechanism of jin through the inter-workings between tendons and bones.
Please also refer to Lee Scheele‘s article. It might also help to read the book The Web That Has No Weaver: Understanding Chinese Medicineby Ted J. Kaptchuk, which explains common TCM (Traditional Chinese Medicine) models of the human body, such as qi, meridians, etc., that are applicable in internal martial arts such as tai chi.