What does 5 of the INT (5) in MySQL mean?

for type int, MySQL supports specifying display width
For example:
Int (5): Indicates that if the numeric width is less than 5 bits, the width is filled and the total width is guaranteed to be 5 bits.
The default is int (11), and with Zerofill you can see the effect.

DROP TABLE IF EXISTS tab_5;

CREATE TABLE Tab_5
(id int (5))
Engine=innodb
DEFAULT Charset=utf8;

INSERT into Tab_5
VALUES (123);

INSERT into Tab_5
VALUES (12345);

INSERT into Tab_5
VALUES (1234567);

ALTER TABLE Tab_5
MODIFY ID Int (5) Zerofill;

mysql> SELECT ID from tab_5;
+---------+
| ID |
+---------+
| 00123 |
| 12345 |
| 1234567 |
+---------+
3 Rows in Set (0.00 sec)

What does 5 of the INT (5) in MySQL mean?