Road Bikes

The term road bicycle is used to describe bicycles built for traveling at speed on paved roads. Some sources use the term to mean racing bicycle. Other sources specifically exclude racing bicycles from the definition, using the term to mean a bicycle of a similar style but built more for endurance and less the fast bursts of speed desired in a racing bicycle; as such, they usually have more gear combinations and fewer hi-tech racing features. Certain of these bicycles have been referred to as 'sportive' bicycles to distinguish them from racing bicycles.
Compared to other styles of bicycle, road bicycles share common features:
The tires are narrow, high-pressure, and smooth to decrease rolling resistance.
They usually use multiple derailleur gears; however, single-speed and fixed-gear varieties exist.
The bicycle is of a lightweight construction.

Road Bikes

Road Bikes

Road Bikes

Road Bikes

Road Bikes

Road Bikes

Road Bikes

Road Bikes

In short I would define a road bike as any bicycle that is meant to be traveled pretty much exclusively on the pavement. When I was growing up, they were often called 10-speeds. Road bikes tend to have narrow tires, "drop"-style handlebars (they curve out and around) and are built for speed. Most modern road bikes are made out of aluminum for a entry-level model and carbon fiber for expensive models. Here is an example of a typical road bike: