What is a static function?

Answer 1

Okey I see, moreover it can be used with an array e.g. static const char arrayOfChar []
Here what is the meaning?

Answer 2

A static function is a function that only must be known in the translation unit it is defined in, i.e. the cpp.
Therefore, if you compile a file with definitions (e.g. a header file) multiple times for a build artifact, the "one definition rule" (ODR) is not violated.
ODR was introduced in C++03 to remove ambiguity when linking multiple binary files that contain functions with the same name but might have different implementations.

Answer 3

A static function *in a class* on the other hand is a function that does not require an object instance of the class to be called.
Unfortunately, as you see, what the static keyword does pretty much depends on the context in which it is used.