In C++, cout is an object of the class ostream and is used to display the output to the standard output device, typically the monitor or screen. It is defined in the iostream header file and is associated with the standard C output stream stdout. The data to be displayed on the screen is inserted in the standard output stream (cout) using the insertion operator <<. For example, cout << "Hello, World!" would display "Hello, World!" on the screen. Additionally, cout can be used with other member functions such as cout.precision(), cout.put(), and cout.write() to format and display data in various ways.

In summary, cout in C++ is a fundamental component of the language used for outputting data to the standard output device, and it plays a crucial role in displaying information to the user.