An aquifer is a geological formation that can store and transmit groundwater, typically composed of permeable materials like sand, gravel, or fractured rock. Aquifers are crucial sources of freshwater for drinking, irrigation, and industrial use. They are recharged by precipitation and surface water, and can be classified as unconfined or confined depending on the presence of impermeable layers above them. Sustainable management of aquifers is essential to prevent depletion and contamination.