The difference between “public” and “public static”?

Question

What does static mean?

I know public means that it can be accessed from outside the class, and private only from inside the class…

Answer 1

An example: when use the static keyword, we cannot use $this

class Foo {
    private $foo='private';

    private function priv_func() {
        echo 'priv_method';
    }

    public static function get() {
        echo $this->foo;
        $this->priv_func();
    }
}

$obj = new Foo();
$obj->get();

Fatal error: Using $this when not in object context in (…)