What is a Segment Tree and how does it support range queries?

Segment trees store interval information for array range queries (sum, min, max) and updates in O(log n). Each node represents an interval; root is [0,n-1], children split the interval in half. Build is O(n), query combines relevant segments in O(log n), and point update propagates up in O(log n). Lazy propagation enables O(log n) range updates by deferring updates to children until needed. Used in competitive programming and databases.