LIFO means Last-In-First-Out, which refers to how stacks operate. The last element to be added is added to the top of the stack, and will also be the first to be removed. This maintains an order to the stack. This is also in contrast to the FIFO, or First-In-First-Out principle, which is how queues operate. If you think of a stack of a book or a real-life queue of people, these principles can be seen in action.