sapient beings

A hybrid species is basically a, sometimes artificial, crossbreed of 2 or more separate species.

To be considered a hybrid species, the species must be able to produce viable offspring within itself, if it can not it is not considered a separate species. Still a crossbreed but not an independent species in itself.

Examples are the Kento who are a crossbreed between a horse (or similar) and a humanoid or the Gryphon which is a crossbreed of three species.