  The Maslov correction to the wave function is to the jump of $-\pi/2$ in the
phase when the system passes through a caustic point. This phenomenon is
related to the second variation and to the geometry of paths, as conveniently
explained in Feynman's path integral framework. The results can be extended to
any system using the semiclassical approximation. The 1-dimensional harmonic
oscillator is used to illustrate the different derivations reviewed here.
