A monopoly is a company that has successfully eliminated all competition. This means that the company can regulate its own prices.
A trust consists of several companies that work together, and later may eliminate other competition. A trust may also regulate prices because the companies involved often agree on the policy.
Court cases were won against monopolies and trusts specifically because of these issues. Citizens were unhappy with monopolies and trusts because they did not have the option to purchase a cheaper version of a certain item. All competition was eliminated, and many families needed to live without the item because they could not afford the monopoly's price.
