Complex sentence: Kozai mechanism, is a perturbation of the orbit of a satellite by the gravity of another body orbiting farther out, causing libration (oscillation about a constant value) of the orbit's argument of pericenter.
Split into simpler sentences: Kozai mechanism, refers to the orbit of a satellite that is perturbed by another body orbiting farther out. Due to the perturbation, the orbit of the satellite experiences libration (oscillation about a constant value) of its argument of pericenter.