It refers to Queue. The first data to be added into the queue will be the first to be removed out from the queue.

It refers to Queue. The last data to be added into the queue will be the first to be removed out from the queue.

It refers to Stack. The first data pushed onto the stack will be the first to be popped out from the stack.

It refers to Stack. The last data pushed onto the stack will be the first to be popped out from the stack.