What are Greenhouse Gases?

According to NASA, greenhouse gases are:

… gases in Earth’s atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere.

THE MAIN GREENHOUSE GASES

•   Water vapor
•   Carbon dioxide
•   Methane
•   Ozone
•   Nitrous oxide
•   Chlorofluorocarbons
  

WHAT IS THE GREENHOUSE EFFECT?