What are stacks and queues?

Stacks and queues are two basic data structures that follow the LIFO (last-in, first-out) and FIFO (first-in, first-out) principles, respectively. Stacks are often used to keep track of the order of function calls, while queues are often used to model lines of people waiting to be served. A stack is a data structure that works like a pile of plates, where the last plate you put in is the first one you take out. A queue is a data structure that works like a line at the grocery store, where the first person in line is the first person to be served.