Linked from
The 12 pages that link to Spin quantum number, each with the reason it gives.
Quantum numberBroader topic: It labels an intrinsic property not explained by orbital motion.
Electron spinRelated: It fixes the magnitude of an electron’s intrinsic angular momentum.
Singlet oxygenRelated: Electron-spin orientations distinguish triplet oxygen from singlet oxygen.
Triplet oxygenRelated: The two unpaired electron spins combine to give oxygen total spin one.