在MySQL中,解释查询的过滤列是什么意思?

mysql> EXPLAIN EXTENDED SELECT * FROM table WHERE column = 1 LIMIT 10;
+----+-------------+----------+------+---------------+--------------+---------+-------+--------+----------+-------+
| id | select_type | table    | type | possible_keys | key          | key_len | ref   | rows   | filtered | Extra |
+----+-------------+----------+------+---------------+--------------+---------+-------+--------+----------+-------+
|  1 | SIMPLE      | table    | ref  | column        | column       | 1       | const | 341878 |   100.00 |       |
+----+-------------+----------+------+---------------+--------------+---------+-------+--------+----------+-------+
1 row in set, 1 warning (0.00 sec)

过滤列的含义是什么?数字是高还是低?是的,我读过文件,但我不太明白数字表示什么,或者什么值被认为是可取的。