Package explain

[Zarathustra]

Could anybody explain what "package" exctly mean?

module package1.module1;
static int variable = 3;

module package1.module2;

module package1.module3;
package import package1.module1, package1.module2;

module main;
import package1.module3;

void main(){ 
  variable1 = 5;  // Why variable is accessable?
}

 |
 |--- main
 |--- package1
           |
           |--- module1
           |--- module2
           |--- module3

I'm dsss user.