From Wikipedia: The C++ Standard Library is a collection of classes and functions, which are written in the core language and part of the C++ ISO Standard itself. The C++ Standard Library provides several generic containers, functions to utilize and manipulate these containers, function objects, generic strings and streams (including interactive and file I/O), support for some language features, and functions for everyday tasks such as finding the square root of a number. Features of the C++ Standard Library are declared within the std namespace.