Definition: A neutrino is a fundamental particle with no electric charge and travels at speeds close to the speed of light. The symbol for neutrino is the greek letter ν.
There are three types of neutrinos, each one associated with a partner particle.
νe = electron neutrino
νμ = muon neutrino
ντ = tau neutrino
Examples: Neutrinos are formed during some types of nuclear decay and when cosmic radiation collides with atoms in the atmosphere.