Infiltration, as it occurs in the water cycle, is the process by which the water on top of the ground enters into the soil. Infiltration is necessary for the sustaining of plant life. Some of the water not used by plants moves deeper into the ground water level.
The rate of infiltration is the speed at which the soil takes in water either from the rain or from irrigation. How quickly the water is absorbed depends upon the type of soil on which it falls, how much water it already has in it, and the intensity of the rain or irrigation process. When the soil is over-saturated, infiltration does not occur.