What is the meaning of first in first out merchandisers?

In this system they have procedures in place so that the first stock of a product received (i.e. first in) will be the first stock of that product sold (i.e. first out). This prevents the accumulation of forgotten old stock in the "back of the warehouse" while the new stock arrives and is immediately sold, reducing waste. The system is utilised fully in dealing with shortlife chilled foods for example that have "use by" and "best best" dates. In most organisations its called stock rotation or variants of the term