Spin is the intrinsic quantum property that gives electrons a half-integer angular momentum.
Electron spin has quantum number one-half. This does not mean the electron is a tiny ball literally rotating in space; spin is an intrinsic form of angular momentum described by quantum mechanics. When measured along an axis, an electron’s spin component can produce two results, commonly labelled spin-up and spin-down.
Spin also gives particles magnetic moments and strongly influences how they behave in atoms, solids and magnetic fields. Electrons are fermions because they have half-integer spin. The connection between spin and particle statistics is expressed by the spin–statistics theorem, while the Pauli exclusion principle determines how electrons fill atomic orbitals.