Percolation is the process by which a fluid moves through a porous medium, such as soil, sand, or rock. The fluid can be water, oil, or gas. Percolation occurs when the fluid is pulled through the pores by the force of gravity. The rate of percolation depends on the size and shape of the pores, the density of the fluid, and the viscosity of the fluid.

Percolation is an important process in the movement of water through the soil. It is also important in the movement of oil and gas through the earth. Percolation can also be used to separate liquids and solids.

The term "percolation" is derived from the Latin word "percolare", which means "to filter".