Answer:  The function PIVOT transposes rows in columns and the function UNPIVOT transposes columns in rows. They have been added in 11g. 

WITH
   T
AS
(
   SELECT
      DEPTNO
   FROM
      EMP
)
SELECT
   *
FROM
   T
PIVOT
(
   COUNT(*)
   FOR
      (DEPTNO)
   IN
      (10,20,30,40)
);

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |     1 |    52 |     3   (0)| 00:00:01 |
|   1 |  VIEW               |      |     1 |    52 |     3   (0)| 00:00:01 |
|   2 |   SORT AGGREGATE    |      |     1 |     3 |            |          |
|   3 |    TABLE ACCESS FULL| EMP  |    14 |    42 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Four columns are created for the departments 10, 20, 30 and 40. For each column, the number of corresponding rows is counted.

Compare with:

SELECT
   DEPTNO,
   COUNT(*)
FROM
   EMP
GROUP BY
   DEPTNO; 

    DEPTNO   COUNT(*)
---------- ----------
        30          6
        20          5
        10          3

In the first statement, one row is returned with all departments. In the second statement each department is on a different row. The columns that are not aggregated and not pivoted will return multiple rows:

WITH
   T
AS
(
   SELECT
      DEPTNO,
      JOB,
      SAL
   FROM
      EMP
)
SELECT
   *
FROM
   T
PIVOT
(
   MIN(SAL) AS MINSAL,
   MAX(SAL) AS MAXSAL
FOR
   (JOB)
IN
   (
      'CLERK' AS CLERK,
      'SALESMAN' AS SALES
   )
)
ORDER BY
   DEPTNO;

    DEPTNO CLERK_MINSAL CLERK_MAXSAL SALES_MINSAL SALES_MAXSAL
---------- ------------ ------------ ------------ ------------
        10         1300         1300
        20          800         1100
        30          950          950         1250         1600

Three rows are selected. The job is the pivot, the salaries are aggregated and the departments are returned as distinct rows. Note the different values for the pivot are explicitly listed.

The inline view T contains three columns, the salary is aggregated, the job is transposed into multiple columns, and the remaining column is used as a group for the aggregation. The remaining column is the department, which contains three distinct values; each value returns exactly one row. To specify the group by the department, it is therefore necessary to select only the department in addition to the aggregated values and to the transposed column.