A highway is a busy road with many lanes. Highways are usually the quickest route for driving between one city and another.
Highways were originally built to connect cities and towns, and since they're wide and have high speed limits, they decreased the travel time. Highways are always considered public land, and they're usually maintained by the individual state. The Old English precursor was heahweg, "main street" or "main way." The word high has often been used to mean "main" or "major," especially when describing a street.