iostream is a header file which is used for input/output in the C++ programming language. It is part of the C++ standard library. The name stands for Input/Output Stream.

In C++ and its predecessor, the C programming language, there is no special syntax for streaming data input or output. Instead, these are combined as a library of functions. Like the cstdio header inherited from C's stdio.h, iostream provides basic input and output services for C++ programs.

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