Corruption is a system that starts out good but somehow goes wrong. The word comes from a Latin word meaning "Rotting". Corruption could be a government doing what they say is good, but instead oppress people, or an official doing something wrong. It can also mean a computer file or computer program which malfunctions or becomes infected with a computer virus. It may also mean an abuse of power, usually for a personal benefit.
Sometimes the term just means bribery.