FIFO (First In, First Out) is an inventory management methodology used in maintenance operations and management. It is based on the principle that the first items to enter into inventory should be the first items to be used or sold. This approach is used to ensure that the oldest items in the inventory are used first, thus avoiding spoilage or obsolescence. FIFO is often used in combination with other inventory management systems, such as Just-in-Time (JIT) and Kanban, to ensure that the right items are available when needed. FIFO is also used to track the cost of inventory used or sold, as costs vary depending on the time they were purchased.