What Is the Mass of a Neutrino?

Neutrino means little neutral particle. We even really knew what it was because that's all we knew about it, that it couldn't be very massive and that it was electrically neutral. So in that sense, you might even be tempted to say that it's a well-named particle. But I guess for us, Daniel, talk to us about what a neutrino actually is. It's so weird and yet so fundamental and at the same time, not a part of the matter around us.