Noble
The Nobles are a race of humans on Scadrial, currently featured in the Mistborn trilogy.
The nobles were effectively created by the Lord Ruler when he forcibly divided the people of the world. The nobles are descendants of the people who supported the Lord Ruler on his rise to power. Due to centuries of (mostly) keeping to themselves, nobles and skaa have basically diverged into two distinct races of humans. All Allomancers have a noble descendant somewhere along their heritage. This is because when the Lord Ruler came to power, he gave his initial supporters beads of lerasium which imparted to them the powers of a Mistborn.
Culture
The life of the nobles is rife with secrecy and plotting. Almost all nobles are driven by gaining money, power, or social prestige.
All nobles are divided among different Houses. Each house has its own agenda and works towards its own betterment. Each house individually has its own political enemies and allies. Generally, leadership of a house is inherited.
Powers
Most (but not all) nobles are Allomancers to some degree. Very few, however, are actual mistborns. This is due to the thinning of Preservation's power through the generations of nobles.