Thread: questions about static function & static const variable

I have some questions (actually two) that really bugging me for a long time.

question #1:
why are some functions declared static?
what is the effect of declaring a function static?

Code:

static void foo (void)
{
  /* blah blah blah... */
}

question #2:
is this function thread safe?

Code:

int foo (int bar)
{
  static const int a_static_const_int = 100;
  int foobar;

  /* blah blah blah... */

  return(foobar);
}

thank you for your attention.