1. The twirling motion of an electron, independent of any orbital motion.
2. The intrinsic half-integer angular momentum of an electron.
3. That property of an electron that gives rise to its angular momentum around an axis within the electron.

Spin is one of the permanent and basic properties of the electron.

1. A resonant absorption of electromagnetic radiation by a paramagnetic substance, having unpaired electrons, when the energy levels are split by the application of a strong magnetic field.
2. Magnetic resonance arising from the magnetic moment of unpaired electrons in a paramagnetic substance or in a paramagnetic center in a diamagnetic substance (a group of substances which in a magnetic field become magnetic in an opposite direction to that of iron or relating to a substance that is repelled by a magnet).

The vector sum of the spin angular momenta of electrons at each point in a substance per unit volume.

A spectrometer or an instrument that produces a spectrum; especially, one in which wavelength, energy, intensity, etc., can be measured based on electron paramagnetic resonance.