What made fascism different from earlier dictatorships was the presence of a mass party that monopolized power through its security services and the army and that eliminated all other parties, using considerable violence in the process. The new style of party was headed by a leader who had virtually unlimited power, was adulated by his followers, and was the focus of a quasi-religious cult. The party's doctrine became an obligatory article of faith for not only its members but for all other citizens and was constantly projected by means of a powerful propaganda machinery.
--Walter Laquer, Fascism: Past, Present, Future (1996) p. 14
Update: What is fascism? by Jon at Exurban League,
By the way, here is Goldberg’s definition [Jonah Goldberg in Liberal Fascism]: “Fascism is a religion of the state. It assumes the organic unity of the body politic and longs for a national leader attuned to the will of the people. It is totalitarian in that it views everything as political and holds that any action by the state is justified to achieve the common good. It takes responsibility for all aspects of life, including our health and well-being, and seeks to impose uniformity of thought and action, whether by force or through regulation and social pressure. Everything, including the economy and religion, must be aligned with its objectives. Any rival identity is part of the ‘problem’ and therefore defined as the enemy.”