This is a GREAT question! Not "what is love?" but "where does it come from?"
I think love comes from our energetic bodies as a spiritual connection to another being. Our energies are vibrating in sync: we are connected energetically. And when we are connected, we feel compassion and empathy, and we only want good things for the other, and their good things raise my energy as welll as theirs.
That is how we can change the planet; connect with and love more people. Raise our collective vibration!