Programmer-ese for "First In, Last Out". Equivalent to LIFO, but easier to say. Describes the order objects are processed in when using a stack. By contrast, a queue is FIFO (First In, First Out).
Also a good way to think about nesting E2 HTML tags -- the first tag you open is the last one you should close(<B><I>...</I></B>). Some browsers (those that stick to strict W3C standards) will fail to close one or both HTML tags at all otherwise.