Where a rolling shutter scans line by line, a global shutter captures the entire frame in one simultaneous moment, much like a mechanical leaf shutter. Fast pans stay straight, propellers stay shaped like propellers, and strobe lighting illuminates the whole frame evenly.
The engineering cost is real. Global shutter designs need extra storage circuitry at every pixel, which historically reduced the light-gathering area and cost a stop or more of dynamic range while raising price. That trade is why the feature stayed confined to industrial, machine-vision, and high-end cinema cameras for years.
Recent sensors have narrowed the penalty enough that global shutter has begun appearing in mainstream mirrorless bodies. It matters most for fast action, drone and gimbal work, LED-wall virtual production, and any application where a strobe is involved. For ordinary handheld shooting a modern fast-readout rolling shutter is usually sufficient.