C++ : What does static mean outside the class or struct ?

file_0.cpp

#include <iostream>

int variable_v0 = 500;

void func_a()
{
	std::cout << "I am func_a" << std::endl;
}

static void func_b()
{
	std::cout << "I am func_b" << std::endl;
}

main.cpp

#include <iostream>

// use static as much as you can if you don't need the variable to be global
// otherwise linker is going to be able to pick it up everywhere.


// extern means it will look for the variable or function in the external translation unit
// which is called external linkage or external linking

extern void func_a(); 
extern void func_b(); 


//static int variable_v0 = 20; 
extern int variable_v0; //500

//int variable_0; // error already defined in other translation unit

int main()
{
	func_a(); // ok linker has found it external translation unit
	//func_b(); // liner error ( in file_0 it's marked as static so it's limeted to that translation unit)

	std::cout << variable_v0;

	return 0;
}