A queue, like a stack, is a data structure based on the linked list concept. Instead of allowing you to add and remove items at a single point, a queue allows you to add items at one end and remove them at the other. In essence, this forms a FIFO data flow: the first item into the queue is also the first item out. This is, of course, the way your to-do list ought to work–the oldest item ought to get handled first. Unfortunately, most people handle their workflow based on the stack data model, not on a queue.