They start out as brand names, but the classics, which are copied by other makers, become design names. The "Tessar" is a Zeiss brand name, for instance, for a particular 4-element/3-group design from 1902, but many Optars, Ektars, Skopars, and even some enlarging lenses are tessar designs. Ektar, however, was a name for the top quality Kodak products, and some Ektars may be tessars, but a few are heliar designs (5-element/3-groups).

This site gives some history on many of the basics:

http://www.panix.com/~zone/photo/czlens.htm

It's kind of annoying to see Cosina using some of these classic names like "Color-Skopar" and "Heliar" on their new Voigtlander-branded lenses, because they are modern designs, largely unrelated to the classic designs. They may be good lenses, but they should get new names.