What is groundwater? What are the sources of water which are fed by groundwater?

If we dig deeper into the soil, then we would reach a depth where the soil-rock gap is filled by water. This is the upper layer and is called water table. The water found below the water table is called groundwater. It varies from place to place.
The sources of water that feed and are fed by groundwater are rivers, lakes and wetlands. The water in these sources come from the water below the water table.