LIFO is an acronym which stans for last in, first out. In computer science and queueing theory this refers to the way items stored in some types of data structures are processed. By definition, in a LIFO structured linear list, elements can only be added or taken off from only one end, called the "top". A LIFO structure can be illustrated with the example of a narrow, crowded elevator with a small door. When the elevator reaches its destination, the last people to get on have to be the first to get off.