Difference between internal data dictionary and table definition file

Hi,

I am an undergraduate student and want to learn about innodb storage
engine. I came up with this line in mysql reference manual that MySQL
server keeps data dictionary information in .frm files which it stores
in the database
directories, whereas InnoDB also stores the information into its own
data dictionary inside the table space files.I want to know , where
comes the difference between InnoDB internal data dictionary and table
definition ( .frm ) files . Do they store the same information about a
table ?
If no then kindly help me by telling what information is stored in one
that is different from other.

Waiting for a response,
Kinaan Khan Sherwani

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