Definition: A data structure is a specialized format for organizing, processing, retrieving and storing data in a computer memory so that it can be used efficiently.

1. Classification of Data Structures:

• Linear Data Structures: Elements are arranged sequentially or linearly (e.g., Arrays, Stacks, Queues, Linked Lists).
• Non-Linear Data Structures: Elements are arranged in a hierarchical or interconnected network fashion (e.g., Trees, Graphs).

Stack: A stack is a linear data structure that follows a particular order in which the operations are performed. The order may be LIFO (Last In First Out) or FILO (First In Last Out).

Queue: A queue is a linear structure which follows FIFO (First In First Out) property. Operations are performed at both ends: Enqueue (Insertion at rear) and Dequeue (Deletion from front).

A linked list is a linear data structure where elements are not stored at contiguous memory locations. Instead, each element (node) consists of a data item and a reference (link) to the next node in the sequence.

Trees: A non-linear hierarchical data structure consisting of nodes connected by edges. Binary Search Tree (BST) is a popular tree variant where the left child is smaller and right child is greater than the parent.

Sorting algorithms rearrange elements in a specific order (ascending or descending). Examples include Bubble Sort, Insertion Sort, Selection Sort, Quick Sort, and Merge Sort.