A tree is a non-linear, hierarchical data structure that consists of nodes connected by edges. Each tree has a root node, which serves as the starting point, and every node can have zero or more child nodes. A node without any children is called a leaf node. Trees are used to represent hierarchical data structures like file systems, HTML DOM, and organizational charts. One of the most common types of trees is the binary tree, where each node has at most two children (left and right). Other types include binary search trees (BSTs), where the left child is smaller than the parent and the right child is larger, and balanced trees like AVL and Red-Black trees, which maintain height balance to ensure efficient operations. Traversal is an essential operation in trees, with common techniques including in-order, pre-order, and post-order traversal. Trees are also used in many algorithms, including Huffman coding, and data structures like heaps (which are a type of binary tree used in priority queues). Mastering trees is fundamental for solving problems related to hierarchical data, sorting, searching, and more.