Perfect competition versus monopoly
The opposite of perfect competition is monopolistic competition. A monopoly is a market structure with one seller but many buyers.
Utilities are a classic example of a monopoly. If your electric company raises rates, you can't just take your business to a competing electric company. Theoretically, an electric company could raise its price to infinity, and your choices would be to either pay the price charged or go without electricity. (Note: In practice, utilities are typically regulated monopolies, and state governments generally have to approve rate increases.) It's also extraordinarily difficult for utility companies to enter and exit a market, given the infrastructure costs and the need to enter into long-term contracts.
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