Meaning of "COUNT STOPKEY" in explain plan

Hi,

Could some one tell the meaning of "COUNT STOPKEY" in explain plan
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| Id  | Operation                    | Name         | Rows  | Bytes | Cost (%CPU)| Time     |
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|   0 | SELECT STATEMENT             |              |   100 |  3700 |     5   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY               |              |       |       |            |          |
|   2 |   TABLE ACCESS BY INDEX ROWID| T1           |   103 |  3811 |     5   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN          | SYS_C0020704 | 90002 |       |     3   (0)| 00:00:01 |
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Regards
Raj