FIFO stands for first-in, first-out, meaning that the oldest inventory items are recorded as sold first but do not necessarily mean that the exact newest physical object has been tracked and sold; this is just an inventory technique.
LIFO stands for last-in, first-out, meaning that the most recently purchased items are recorded as sold first. Since the 1970s, U.S. companies have tended to use LIFO, which reduces their income taxes in times of inflation.[1]
The difference between the cost of an inventory calculated under the FIFO and LIFO methods is called the LIFO reserve. This reserve is essentially the amount by which an entity's taxable income has been deferred by using the LIFO method.
LIFO liquidation
Notwithstanding its deferred tax advantage, a LIFO inventory system can lead to LIFO liquidation, a situation where in the absence of new replacement inventory or a search for increased profits, older inventory is increasingly liquidated (or sold). If prices have been rising, for example through inflation, this older inventory will have a lower cost, and its liquidation leads to the recognition of higher net income and the payment of higher taxes, thus reversing the deferred tax advantage that initially encouraged the adoption of a LIFO system. Some companies who use LIFO have decades-old inventory recorded on their books at a very low cost. For these companies a LIFO liquidation results in an inflated net income (and higher tax payments). Companies can use liquidations to manage their earnings.
Also mobile telecom operators either use FIFO or LIFO to allocate remaining call credit a customer did not fully use in a billing period. In telecom terms FIFO is good for the customers while LIFO is good for the telecom