A library is a collection of classes and functions that are defined for easy use and reference. We can include these in our programs using header files.

We've never defined cout when writing our programs, but it's been declared for us in the <iostream> header file!

It's also been defined in the C++ support library, which is linked to our program during runtime.

Are you sure that's right? Think about what we've been using throughout the course to output text.