This lecture discusses aquifers, which are underground layers of water-bearing permeable rock or sediment that store and transmit groundwater. There are two main types of aquifers: confined and unconfined. Unconfined aquifers, also known as water table or phreatic aquifers, receive water directly from the surface, while confined aquifers are trapped between impermeable rock layers. The water table marks the upper surface of the zone of saturation, where all pore spaces are filled with water, whereas the vadose zone above it contains both air and water. Additionally, the capillary fringe is a subsurface layer where groundwater moves upward from the water table by capillary action.