The Azimuthal quantum number (or orbital angular momentum quantum number) symbolize as l (lower-case L) is a quantum number for an atomic orbital that determines its orbital angular momentum. The azimuthal quantum number is the second of a set of quantum numbers (the principal quantum number, following spectroscopic notation, the azimuthal quantum number, the magnetic quantum number, and the spin quantum number) which describe the unique quantum state of an electron and is designated by the letter l.