Quantum Number: A value used to describe the energy levels available to atoms and molecules; includes principal (n), azimuthal (l), magnetic (m_l), and spin (m_s) quantum numbers.
Electron Orbital: A region around an atomic nucleus where an electron is likely to be found; each type of orbital has a specific shape and orientation.
Pauli Exclusion Principle: \text{A principle stating that no two fermions can have identical quantum numbers within the same system. For electrons in an atom, this means no two electrons can occupy the same state simultaneously.}