This is the gazelle of bicycles, built as it is for speed. Everything is focused around going as fast as possible, whilst racing up hill and down dale on the same roads as used by cars. (For purpose-built cycle tracks there are yet more sleek rides.) But commonly a road bike will be extremely lightweight, using thinner gauge steel or aluminum tubing, or even a carbon fiber blend.
The tyres will most likely be very thin, reflecting their ability to hold higher tyre pressure, which in turn reduces rolling resistance. A road bike's handlebars normally allow the rider to assume low front profile so they become more aerodynamic. The gear ratio's will be close together -- to ensure you find that perfect pedal rhythm or cadence that helps cover long distances with an economic use of energy.