The *(political term) for the situation where a person, company, or trust, controls a market.

Two kinds of monopoly must be distinguished and opposed: <em>de jure</em> monopoly and <em>de facto</em> monopoly:
<ul>
<li>In a de jure monopoly, the law, or some external force, constrains everyone to use the monopolist as the sole provider of some service, a priori.
<li>In a de facto monopoly, although everyone is free to choose one's own provider for said service, it so happens that everyone or almost everyone consumes services from the same provider, a posteriori.
</ul>

De jure monopoly are the worst way in which competition can be unfair, leading to degenerating, unproductive, uninnovative, unadapting _(tradition)s, which benefits only to the tenants of the monopoly, bitterly harming the entire system. Even when there are laws against monopolies in general, the mere existence of the de jure monopoly is the sign that even stronger laws actually support the monopoly by granting special privileges or subsidies to one provider (e.g. "intellectual property" law, law-enacted corporations, "public service" law, etc.)

De facto monopolies are the result of _(fair competition), whereby some provider is so good that the marginal benefit of changing to a new better one (if exists) is lower than the transaction cost involved in such a change. They can result but from constant adaptation and innovation from the market leader to prevent the emergence and growth of the virtual or real competition towards which customers will turn the very moment that they can expect better service/cost combination from another provider. Anti-monopoly laws, when they hamper the progress of de facto monopolies, are actually making the competition less fair, not fairer, since they promote inferior competitors and slow down the superior one. 

As far as _(operating system) design applies, _(kernel)s can be seen as execution-time de jure monopolies of code, that every _(process) calls so as to achieve common services and communication; their effect, as expected, is to slow down services and communication (they do bring some "safety", but then, for most uses, they bring less safety and have higher cost than compile-time solutions). On the other hand, successful libraries are de facto monopolies of code, that everyone calls because when benefits and tradeoffs are considered, it overall costs much less to use them than to use competing libraries or to roll one's own code.
