In the context of precision guided munitions, space launch vehicles, and sometimes remotely operated vehicles, the midcourse is that part of the vehicle path that manages the path between what may be a sometimes highly dynamic boost phase, and possibly multiple phases of terminal guidance. It may be no more than a straight-line path after stabilizing from the strong forces of launch (general vehicle) to the final area where its approach and terminal guidance comes into play, or it may involve a number of turns either preprogrammed or based on information from sensors.
With ballistic missiles, midcourse guidance involves stabilizing the path, through air and space, after burnout of the boost engines and the end of increasing acceleration. Stabilization most often depends on small rocket motors called thrusters, but also may use gyroscopes, and aerodynamic fins while still in atmosphere. Midcourse guidance for a high-altitude cruise missile or unmanned aerial vehicle usually depends on inputs from Global Navigation Satellite Systems (e.g., GPS) or sometimes inertial navigational, and adjusts its flight path with aerodynamic control surfaces and possibly adjustments to its engine power. Terrain-following cruise missiles may also use GPS or intertial guidance, but they also make significant use of radar, minimally a radar altimeter for terrain avoidance, but often terrain contour mapping systems that match the ground radar image to a highly accurate digital map.