orbital angular momentum

The Azimuthal quantum number (or orbital angular momentum quantum number) symbolized as l (lower-case L) is a quantum number for an atomic orbital which 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.
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The angular momentum of, for example a planet moving around the sun, or (simplistically) an electron orbiting the nucleus in an atom. In the sub-microscopic world inside an atom the angular momentum can only take fixed (quantised) values which are integer multiples of Planck's constant, h. [ang. mom. = mvr = nh/2pi]. See also angular momentum.