MySQL 5.5 Release Notes
MySQL stores its data dictionary information for tables in
.frm files in database
directories. Unlike other MySQL storage engines,
InnoDB also encodes information about the table
in its own internal data dictionary inside the tablespace. When
MySQL drops a table or a database, it deletes one or more
.frm files as well as the corresponding
entries inside the InnoDB data dictionary. You
cannot move InnoDB tables between databases
simply by moving the .frm files.