A monopoly is when a single company gets so big that they control the market to the point where they have an "unfair" advantage. In other words, competition is pointless. It's easier for the consumer to just lie down and take whatever the monopoly gives at whatever price they want.
Example? Just look down. If you're wearing pants you probably have a zipper. I'll bet you a dollar that this zipper has "YKK" on it. That's because it was made by the YKK Group. They have a zipper monopoly. The even have a monopoly on the machines that make the zippers. They're into other things but they control the zipper market.
People don't complain because people don't buy zippers. It's the clothing companies that buy zippers and they don't complain for the same reason you didn't complain about Microsoft's Windows in the 90's or Monsanto's corn today or InBev's beer tomorrow: the price doesn't hurt enough to do something about.