Definition of an empire

From "The Player of Games" by Iain M Banks:

Empires are synonymous with centralised - if occasionally schismatised - hierarchical power structures in which influence is restricted to an economically privileged class retaining its advantages through - usually - a judicious use of oppression and skilled manipulation of both the society's information dissemination systems and its lesser - as a rule nominally independent - power systems. In short, it's all about dominance.