Straight out of the manual:
Example 4-2 Splitting a Column Heading
To give the column ENAME the heading EMPLOYEE NAME 
and to split the new heading onto two lines, enter

SQL> COLUMN ENAME HEADING 'Employee|Name'

Now rerun the query with the slash (/) command:

SQL> /

SQL*Plus displays the following output:

           Employee
Department Name           Salary Commission
---------- ---------- ---------- ----------
        30 ALLEN            1600        300
        30 WARD             1250        500
        30 MARTIN           1250       1400
        30 TURNER           1500          0