A nasty road and sidewalk hazard that develops in the late fall or early spring in the cooler parts of the world. Rain falls on cold asphalt and freezes where it hits, somewhat slowly so that no air bubbles are trapped in the ice.

This ice is extremely slick, yet almost invisible. During the day, it appears on the road as a darker patch of concrete. During the night, it does not reflect your headlights, hence the name black ice. Slipping on a patch while walking is an easy way to get a concussion, or worse.