When I was using a search engine to find out more about myth & legend, I "accidentaly" found something cool!

The division of Greek mythical creatures into two main categories is purely for organization purposes. These categories - "hybrids" and "monsters" - serve to distinguish between different types of mythical beings.

Hybrids : a hybrid is a composite creature - examples are the centaur (combination of human and horse), and the harpy (human and vulture); these mythical beings populated the imaginations, literature, and art of the ancient Greeks.

Hybrids included: centaur, cockatrice, giants, griffin, harpy, satyr (faun) and sirens.

Monsters : the monsters section mainly features beings that are singular entities - in other words, there is but one Minotaur, Medusa, or Pegasus in Greek mythology; monsters were generally either friends or foes to various Greek heroes.

Monster included: Argus, Cerberus, Charybdis, Chimera, Cyclops, Hydra and etc...

There's still more to explore...