Meaning of Cost, Cardinality/Rows,Bytes and time in Explain Plan.

What does the following terms in the Explain Plan mean:
1. Cost
2. Cardinality/Rows
3. Bytes
4. Time
Please give examples.


SQL> create table t as select * from all_objects;
Table created.
 
SQL> exec dbms_stats.gather_table_stats( user, 'T', method_opt=>'for all indexed columns');
PL/SQL procedure successfully completed.
 
SQL> create index t_idx on t(object_id);
Index created.
 
SQL> exec dbms_stats.gather_index_stats( user, 'T_IDX' );
PL/SQL procedure successfully completed.
 
SQL> select * from t where object_id = 42;
Execution Plan
----------------------------------------------------------
Plan hash value: 470836197

-------------------------------------------------------------------------------------
| Id  | Operation                                            | Name  | Rows  | Bytes | Cost (%CPU)| Time        |
-------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                          |          |   557     | 52915 |            9   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID   | T        |   557     | 52915 |            9   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN                       | T_IDX |   223     |            |            1   (0)| 00:00:01 |
-------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_ID"=42)

or in 9i
Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT Optimizer=ALL_ROWS (Cost=2 Card=482 Bytes=44826)
   1    0   TABLE ACCESS (BY INDEX ROWID) OF 'T' (TABLE) (Cost=2 Card=482 Bytes=44826)
   2    1     INDEX (RANGE SCAN) OF 'T_IDX' (INDEX) (Cost=1 Card=193)