REF CURSOR in Oracle PL/SQL

A REF CURSOR is basically a data type.  A variable created based on such a data type is generally called a cursor variable.  A cursor variable can be associated with different queries at run-time.  The primary advantage of using cursor variables is their capability to pass result sets between sub programs (like stored procedures, functions, packages etc.).
Let us start with a small sub-program as follows:
declare
  type r_cursor is REF CURSOR;
  c_emp r_cursor;
  en emp.ename%type;
begin
  open c_emp for select ename from emp;
  loop
      fetch c_emp into en;
      exit when c_emp%notfound;
      dbms_output.put_line(en);
  end loop;
  close c_emp;
end;
Let me explain step by step.  The following is the first statement you need to understand:
  type r_cursor is REF CURSOR;
The above statement simply defines a new data type called "r_cursor," which is of the type REF CURSOR.  We declare a cursor variable named "c_emp" based on the type "r_cursor" as follows:
  c_emp r_cursor;
Every cursor variable must be opened with an associated SELECT statement as follows:
  open c_emp for select ename from emp;
To retrieve each row of information from the cursor, I used a loop together with a FETCH statement as follows:
  loop
      fetch c_emp into en;
      exit when c_emp%notfound;
      dbms_output.put_line(en);
  end loop;
I finally closed the cursor using the following statement:
  close c_emp;