Abbreviation meaning "First In, First Out".
In Forex trading it refers to an order queue structure where all positions opened within a particular currency pair are liquidated (closed) in the order in which they were originally opened.
In accounting it refers to a method for inventory whereby, quite literally, the inventory is assumed to be sold in the chronological order in which it was purchased.
In asset-management it's a valuation method in which the assets produced or acquired first are sold, used or disposed of first.
Opposite to LIFO