The Standard Template Library (STL) is a powerful and comprehensive collection of generic algorithms, data structures, and iterators, that are part of the C++ Standard Library. It was first introduced in the C++98 standard and has been updated in subsequent standards.

The STL provides a set of container classes (such as vector, deque, list, set, map, and others), which are implemented using templates, and can store various types of data. The containers provide a convenient way of managing and manipulating collections of elements, such as arrays, lists, and trees.

In addition to containers, the STL also includes a wide range of algorithms, such as sorting, searching, and manipulating sequences of elements, that operate on the containers. These algorithms are implemented using iterators, which provide a uniform way of accessing the elements in a container, regardless of its underlying implementation.

The STL is widely used in C++ programming due to its simplicity, flexibility, and efficiency. It provides a standard, consistent, and reusable set of components that make it easier to write high-quality and efficient code.