Electrons have an intrinsic angular momentum that is similar to what would be observed if they were spinning. Electron spin is sometimes called a "twoness" property because it can have two values, referred to as "spin up" and "spin down". Nuclei can have spins of their own.
SPIN
Meaning of SPIN in English
General chemistry English glossary. Английский глоссарий общей химии. 2012