Flux pinning is the phenomenon in type-II superconductors where penetrating magnetic flux lines (Abrikosov vortices) are trapped or immobilized by structural defects or inhomogeneities within the material, known as pinning centers. As a core academic concept and research area in condensed matter physics, it investigates the fundamental interactions between vortices and these defects, the mechanisms governing vortex motion and immobilization, and methodologies for enhancing the pinning force. This concept is critical for achieving high critical current densities and stable superconducting behavior required for technological applications of superconductors in magnetic fields, such as high-field magnets, superconducting wires, and energy storage devices.