Quantum spin is a mathematical construct applied to all elementary particles, including photons and electrons. It is called imaginary because electron particles have no size so there’s nothing to spin. And if it had a size, its edges would be moving faster than light for the observed spin rate, so when current physics says that photons and electrons spin, nothing really spins because they are points with no extent. But in this model, they do vibrate outside our space, so a photon for example is a sine wave structure that can really spin on its movement axis.
QR3.7.1. The Curious Case of Quantum Spin
QR3.7.2. Quantum Space
QR3.7.3. Polarization