The Standard Template Library (STL) is a powerful set of C++ template classes and functions that provide common data structures and algorithms. It includes components like vectors, lists, sets, and maps, which help manage collections of data efficiently. STL also offers algorithms for sorting, searching, and manipulating these data structures, making programming easier and more efficient. STL promotes code reusability and flexibility by allowing developers to use generic programming techniques. This means that the same code can work with different data types without modification. By leveraging STL, programmers can focus on solving problems rather than implementing basic data structures and algorithms from scratch.