A typical webcam on a webcam captures video at 720P - which produces images that measure 1280x720 pixels (so less than one megapixel). A 4K webcam captures video at 3840 x 2160 pixels (or just over 8 megapixels). So from a resolution point of view, a 4K webcam is over 8x better.
Other video resolutions offered by webcams are shown in the following table: