The letters "FIFO" refer to:

Stock rotation

Federal Foreign organism inspection

A management plan

Food regulation

FIFO means first in first out, it is used for estimating the the value of inventory at the end of an accounting period. Given the options I'd assume food regulation or stock rotation.

Stock rotation

Explanation:

FIFO means first in first out and it refers to an inventory management method in which the assets bought or produced first are the first ones to be sold or used. This method allows a company to keep the most current costs in the records because the last products acquired are the ones that are supposed to be in stock. According to this, the answer is that the letters "FIFO" refer to stock rotation.