Megacorporation
Megacorp is a term popularized by William Gibson derived from the combination of the prefix mega- with an abbreviation of the word corporation. It has become a term popularly used in cyberpunk literature. It refers to a corporation that is a massive conglomerate, holding monopolistic control over multiple markets (thus, it exhibits both horizontal and vertical monopoly). Megacorps are so powerful that they can ignore the law, have large (military-sized) security forces, hold territory, and possibly even act as a government.
As of 2004, it is doubtful whether any true megacorps currently exist in the real world. Even the largest multinational corporations (MNCs) do not possess anywhere near the same level of power seen in the megacorps of cyberpunk literature. Though powerful, even such corporations as Microsoft or De Beers do not control unbreakable monopolies in multiple, unrelated markets, and the extent to which they are able to flout laws is debated. Historically, there have been similarities between megacorps and the trading companies of the 17th and 18th century mercantilist period, such as the British East India Company.
The land within Walt Disney World is part of the Reedy Creek Improvement District which allows the Disney Corporation to exercise quasi-governmental powers over the area.
In cyberpunk literature, megacorps often play the role of antagonists, and the conflict of the plot is often provided by the struggle of the protagonist against one or more megacorps.
The collectible card game Netrunner explicitly pits one player, a netrunner (a futuristic version of a computer hacker), against another player, who represents a megacorp.