That usage is often called "generic". Note that "a" can, interestingly, be used in the same way. "A lion is a dangerous foe" or "The lion is a dangerous foe". This range of usage of definite (and indefinite) articles is part of well known variation and historical change, if you look up some of the trends of development. The meaning of "definite" is somewhat unclear because there are specific, generic, context-established, etc., meanings.