Final answer:
A small group of companies dominating an industry is known as an oligopoly, characterized by a few large firms controlling the market, unlike a monopoly which is control by one firm or a conglomerate which is a company owning diverse businesses.
Step-by-step explanation:
A small group of companies that dominate an industry is called an oligopoly. This market structure occurs when a market is controlled by a few large firms, which often possess significant market power. In contrast, a monopoly exists when just one firm has full control over an industry. A conglomerate, on the other hand, is a corporation that owns a collection of smaller companies in unrelated industries. In the case of oligopolies, firms may engage in collusion, an illegal practice where they cooperate to act like a monopolist by reducing output and raising prices, leading to higher profits.
An example of oligopoly was the concern in the mid-90s that Microsoft had a disproportionate control over the choices and prices of computers, raising concerns about monopolistic practices, although it was actually part of an oligopoly in the tech industry.