What are LIFO & FIFO? What are they used for?

FIFO means First In First Out, usually used for FMCG and other perishable products 

LIFO means Last In First Out, it's used with items that do not have an expiry date. 

Fun Fact: I always try to be one of the last people to go to the boarding counter and so that my luggage goes in last, because airplane baggage loaders use LIFO system. Which means last baggage in would be the first out! :)