In a C++ program, a *symbol*, for example a variable or function name, can be declared any number of times within its scope, but it can only be defined once. This is the One Definition Rule (ODR). A *declaration* introduces (or re-introduces) a name into the program. A *definition* introduces a name and, in the case of a variable, explicitly initializes it. A *function definition* consists of the signature plus the function body. A class definition consists of the class name followed by a block that lists all the class members. (The bodies of member functions may optionally be defined separately in another file.)

You can force a global name to have internal linkage by explicitly declaring it as **static**. This limits its visiblity to the same translation unit in which it is declared. Note that in this context, **static** means something different than when applied to local variables.