In atomic physics, the magnetic quantum number is the third of a set of quantum numbers (the principal quantum number, 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 m. The magnetic quantum number denotes the energy levels available within a subshell. This quantum number indicates the possible orientation of orbital in space. The value of 'm' for a particular value of 'l' varies from +l to -l including zero.