The water table is the boundary between an unsaturated zone and saturated zone underground.
Because different materials absorb water to a greater or lesser extent, some layers of the crust can be filled with water while other, even higher, levels are not filled at all or are only partially filled.
The saturated zone refers to a layer of rock whose pores are full of water. Pores in the unsaturated zone are empty, or partially filled. The water table figuratively separates the two zones.
Knowing the depth of the water table in any given area helps when deciding what plants, crops, or trees to grow; how far you might have to dig a well to reach a constant supply of water; or whether a building will have a solid foundation.
A layer of porous rock, the aquifer, holds groundwater between two layers of impermeable rock. Rain falling on the surface seeps down to add to the groundwater.
The level of water in the aquifer is called the water table.