The difference between a stack and a queue is that a stack is a last-in, first-out (LIFO) data structure, while a queue is a first-in, first-out (FIFO) data structure. An example of when to use a stack is when you need to implement an undo function, while an example of when to use a queue is when you need to process items in the order they are received, such as with printing jobs or customer service requests.