A stack is a linear data structure that operates on the Last In, First Out (LIFO) principle. This means that the last element added to the stack is the first one to be removed, similar to a stack of plates where you can only take the top plate off. Stacks are widely used in various applications, including function call management, expression evaluation, and backtracking algorithms. The basic operations of a stack include 'push' (adding an element to the top), 'pop' (removing the element from the top), and 'peek' or 'top' (viewing the top element without removing it). Stacks can be implemented using arrays or linked lists, with both implementations offering O(1) time complexity for push and pop operations. One common use of stacks is in managing function calls during program execution, where each function call is pushed onto the call stack, and when a function completes, it is popped off the stack. This allows for efficient backtracking in algorithms, as you can easily return to the previous state. Stacks are also used in parsing expressions, where operators and operands are processed in a specific order to evaluate expressions correctly. For example, in infix notation, operators must be processed based on their precedence, and stacks help manage this order efficiently. Additionally, stacks play a vital role in algorithms like depth-first search (DFS) in graph theory, where you explore paths until you reach a dead end, then backtrack using the stack to explore alternative paths. Overall, understanding stacks and their applications is crucial for mastering data structures and algorithms, as they form the foundation for many complex systems.