Neutrino oscillation is a fundamental quantum mechanical phenomenon where a neutrino, initially created with a specific lepton family number, changes its flavor as it propagates through space. This process implies that neutrinos possess non-zero mass, which allows them to transition between different states.
As a neutrino travels, the probability of detecting it as one of the three known lepton flavors—electron, muon, or tau—varies over time. This oscillation is a direct consequence of the mismatch between the neutrino's flavor eigenstates and its mass eigenstates, a defining characteristic of modern particle physics.