Highways are long strips of flat land that are used by players on 0b0t to travel to long distances without rough terrain. There are 4 Axis Highways that usually start at (0, 64, 0) in Overworld (doubled at spawn at y=128) or (0, 120, 0) in Nether and run along their respective axis both in the Overworld and Nether respectively. There are no prolonged highway sections in The End because of low population density. The highways are distinguished by being mostly made out of obsidian blocks in the center with many patches of other blocks of varied width.
The intended goal of these central highways is to not only provide easy transportation to all players but also to reach the world border in the case of the nether highways, as three of them have already (Z- is yet to). These highways all have varied length and are not the exactly the same. The other highways are usually shorter then their axis counterparts and can vary in material, length, and even direction. Highways also have plenty of "exits" or other passages branching off to other destinations or dead ends. Even with large amounts of destruction, highways still manage to be distinguished and followed, as well as being fixed and maintained regularly by any player that feels inclined to do so.
These are different types of highways (other than regular highways) that can be found throughout the server.
A smaller highway that is made of less conventional materials that branches off of, or somehow connects to a larger highway. Their lengths and widths can vary. Their destinations are not usually clear (unless specified) and can just lead to the middle of nowhere.
A road is a narrow path that is usually isolated from the rest of the road network, but can be connected to a larger access. Their destinations also vary.