Greenhouse Effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.
To simple , the greenhouse effect is the heating of earths surface and atmosphere from solar radition being absorbed and emitted by the atmoshphere, mainly by water vapor and carbon dixode.