Deregulation is when the government seeks to allow more competition in an industry that allows near-monopolies. For example, in the 1990's, the electric utility industry began to be deregulated to allow competition. In some cases this in fact occurred successfully. However, fraud occurred with a company called Enron, which essentially ended any further efforts to deregulate. Enron's fraud also hurt investors' confidence in the stock market, and led to the Sarbanes-Oxley Act of 2002.
On the other hand, the telecommunications and airlines industries were more successfully deregulated. This allowed more competition, and eventually lower prices for these services. However, many companies that could no longer compete went out of business, which had a negative effect on the economy.