Imperials are the native race of Cyrodil, the province in which the Oblivion crisis takes place. Imperials are a human race, like the Bretons and Nords. Imperials are also the most lucrative race; In fact, Tiber Septim, the Ninth Divine, was an Imperial himself. They have proved to be shrewd diplomats and trader and are skilled with heavy armor and have extraordinary social skills. They tend to favor the warrior class.
In the Elder Scrolls series, Imperials are an all around race. They get a bonus to every combat related skill, excluding marksman and endurance. They are a great choice for a person new to the game itself.