The story
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A highway with grade-separated crossings (rather than level crossings) and designed (and only permitted) for high-speed motor-traffic (in Europe motor vehicles with a higher speed limit than 40 km/h) running in two directions on one separate carriageway each. Full definition →
Etymology from Wiktionary, CC BY-SA 4.0.