dictionary.com
high·way
n. Abbr. hwy. or hgwy.
A main public road, especially one connecting towns and cities.
m-w.com
high·way
Pronunciation: 'hI-"wA
Function: noun
: a public way; especially : a main direct road
wikipedia
A highway is a major road within a city, or linking several cities together. It includes roads known as interstate highway, freeway, motorway and autobahn, where a full description varies by country. Generally, a highway is a road which has multiple lanes of traffic in each direction, often with a physical division (median) between opposing traffic, and separate access ramps to and from the highway which are more widely separated than connections on a standard road and are often grade-separated. A highway may prohibit access by pedestrians and limit what vehicles may travel on it.
Historically, a highway was any major road travelling a long distance outside of a city. Early roads between cities would sometimes suffer from highwaymen who would rob people travelling the route.
In the 20th century, however, the word generally came to be used only for high-speed, often specially-designed automobile routes. On 10 September 1913 the first paved coast-to-coast highway opened in the US.
Highways usually have a higher speed limit than other roads because they have additional lanes and are designed for driving at a higher speed. In remote areas, a highway may have rest areas where motorists may stop and relax before resuming a long drive.
By convention, the lane nearest the median on a multi-lane highway is called the passing lane.
The United States has a vast network of national highways (Interstate highways) linking the different states together, as does Australia albeit on a much smaller scale and mostly concentrated on the southeast coastline. Some highways, like the Pan-American Highway or the European routes, bridge multiple countries. With the latter a single road will have several national designations in addition to the European one.
Probably the most famous highway in the United States is Route 66, as immortalised in the song "(Get Your Kicks On) Route 66", while if one follows Australia's Highway 1 the driver can travel from state capital to state capital, almost the entire way around the whole country.