Fairing

From CycleChaos

A fairing is a structure whose primary function is to produce a smooth outline and reduce drag. These structures are generally light-weight shapes and covers for gaps and spaces between parts of a vehicle. They are commonly used on sportbikes to give them smooth lines and make them more physically appealing. There's no doubt they help to reduce drag, however, and often make a bike more rideable (keep less wind of the rider) at higher speeds.