The document discusses stacks, which are linear data structures that follow the LIFO (last in, first out) principle. Stacks can be implemented using arrays or linked lists. Elements are inserted and removed only from one end, called the top of the stack. Insertion is called pushing and removal is called popping. Stacks are used extensively in computer systems, for example in operating system function calls and interrupt handling. The Java programming language contains a Stack class that can be used by programmers.