In economics monopoly and competition signify certain complex relations among firms in an industry. A monopoly implies an exclusive possession of a market by a supplier of a product or a service for which there is no substitute.
Think of it as an Airline that has an exclusive route from x to y. They can charge whatever they want since there is no other carrier flying that route. Air Canada is famous for that. Let's say three Airlines fly from point x to point y.
Let's also assume that Alaska Airline (or any other of your choosing) has the same route but Alaska Airline is cheaper. Air Canada will undercut these prices at a great loss to get rid of the competition and immediately raises the prices.