difference between procedure and function in oracle code example

Example: oracle procedure as vs is

FUNCTION sal_ok (salary REAL, title VARCHAR2) RETURN BOOLEAN IS
   min_sal REAL;
   max_sal REAL;
BEGIN
   SELECT losal, hisal INTO min_sal, max_sal FROM sals
      WHERE job = title;
   RETURN (salary >= min_sal) AND (salary <= max_sal);
END sal_ok;