The neutrino belongs to the family of leptons and is color neutral and electrically neutral. The only force it reacts to is the weak force. Because of this it can travel through large amounts of matter, through our earth for examle, without changing direction. This also makes it very difficult to track a neutrino. The neutrino has hardly mass.

Pauli "invented" the neutrino to conserve the energy during the beta decay. Fermi liked this idea and named it neutrino: little neutral one. It wasn't until about 25 years later that the first neutrino was tracked.

Story of the neutrino More about the neutrino

About Neutrino in German. (Neutrino)