Define "ballet"

The debate about whether ballet is dying or evolving is based upon a fundamental difference in how the debaters define ballet. In genetics, it is slightly clearer when a new species arises. But how to define the point of speciation in the dance world? Does the term "ballet" evolve with the dance, or does it remain lodged in the Classical Era, the Neoclassical Era, or whatever other Era that is not now, while the dance itself continues to morph with the times?