What is the difference between normal and oblique shock waves?

Normal shocks occur perpendicular to flow direction with flow becoming subsonic after the shock, maximum pressure rise, and highest entropy increase. Oblique shocks form at an angle to the flow (determined by deflection angle and upstream Mach number), allowing the flow to remain supersonic after the shock with lower losses. Oblique shocks turn the flow direction, have weaker property changes, and are more efficient for compression. Inlet designs use oblique shocks in series to compress air more efficiently than a single normal shock.