A tele lens consists of a tube attached to a camera at one end, and a lens (group) at the opposite end.
That makes for a rather long lens in that the lens (group) is a little further away then intended focal length, so that Aperture can be placed there where the optical lines cross.. i.e a 400mm tele lens will have the lens (group) a little more than 400mm away from the film (or sensor).
For example, lenses such as the Novoflex 400mm F5.6, Leitz Telyt (Leica) 400mm F6.3, Zeiss Tele Tessar (Hasselblad Series), and other such vintage lenses.
Where as the ZEISS SONNAR ( Hasselblad series ) is a Long Focus lens.
Due to tele lens designs being long and slow, designers went a different route resulting in the long focus lens, which consists out of a tub_ with several lens (groups) divided throughout the tube, enabling designers to make corrections, improving on light gathering power (faster lenses), color rendition, curvature of field, coma,etc. In all, a better lens — although substantially heavier .
Compare the Sigma 400mm F5.6 (Long Focus) with the aforementioned Novoflex 400 F5.6 (Tele Lens) and one will see that the Sigma is physically a good deal shorter and smaller in diameter, yet of the same optical length and speed as the Novoflex.
Difference between Telephoto lens vs. Long Focus lens is Purely defined by their Construction.
Both do the same job ( bring a distant object closer ) so without referring to construction they could be described as Tele lenses.
The word "tele" is older than Lenses; the words "long focus" came into being with lenses.
Hope this helps.