The static storage class specifier

Objects declared with the static storage class specifier have static storage duration, which means that memory for these objects is allocated when the program begins running and is freed when the program terminates. Static storage duration for a variable is different from file or global scope: a variable can have static duration but local scope.

The keyword static is the major mechanism in C to enforce information hiding.

C++ enforces information hiding through the namespace language feature and the access control of classes. The use of the keyword static to limit the scope of external variables is deprecated for declaring objects in namespace scope.