A blood bank is a facility that collects, tests, processes, and stores blood and its components for transfusions. These facilities ensure that donated blood is safe and available for patients in need, such as those undergoing surgery or suffering from medical conditions like anemia. Donors voluntarily give blood, which is then screened for infectious diseases and categorized into different types, such as A, B, AB, and O. Blood banks play a crucial role in healthcare by maintaining an adequate supply of blood, which can be lifesaving in emergencies and for patients requiring regular transfusions.