Noob question - MOVE block

Hello,
First of all sorry for my basic understanding of the Step7 PLC programming.
in a give programm that runs on a Siemens CPU314 i have a move block (see attached picture) that moves the information of the "IB7" input to the MB35 output.
My question is the followings:
1) from where does the IB7 input is comming from? I can not find any other references of this input in the Step7 programm.

Thank you.

I 7.0 to I 7.7
transferred to
M 53.0 to M 53.7

IB, IW, ID are ways to adress groups of inputs the same way one adresses ranges of merkers with MB, MW, MD.

Thank you!
Regards.