In many databases, when you see something like int(11), you would expect 11 to be the maximum size of the field but for some reason the MySQl folks thought that was too intuitive so they decided to change it. In MySQL when you something like int(M), M stands for “Maximum Display Size”.
"M indicates the maximum display width for integer types. The maximum legal display width is 255."
Reference:
Mysql Websites
http://dev.mysql.com/doc/refman/5.0/en/numeric-type-overview.html
Other Resources
http://www.dbforums.com/mysql/1624054-int-m-mysql-what-does-m-mean.html