Based on ElectroMagnetic (EM) theory and the monopulse radar angle measurement principle, the formulae of angular glint for complex target are proposed and generally applied to tackling practical problems. The inherent relations among the three representations of radar angular glint, i.e. the phase-front distortion concept, the energy-flow tilt concept, and the monopulse radar angular noise concept, are clearly demonstrated. The two existing concepts of angular glint are also revised. Thus, a firm theoretical foundation for understanding, modeling, simulating and suppressing the angular glint from complex radar targets is established.