Spun yarns are produced by twisting (spinning) spun fibers (staple fibers) together. Different processes are used depending on the type of fiber (natural fiber, chemical fiber).
Source:
Eberle, Hannelore; Gonser, Elke; Hornberger, Marianne; et al. (2022), Fachwissen Bekleidung, 12. Auflage, Haan-Gruiten: Verlag Europa-Lehrmittel, S. 56