Censorship is when an authority (such as a government or religion) cuts out or suppresses communication.
This has been done widely. All countries, religions and societies have their limits as to what can be said, or written or communication by art or nowadays by computer.
Certain facts are changed or removed on purpose. This may be done because it is considered wrong, harmful, sensitive, or inconvenient to the government or other authority. This can be done for different reasons.