It is the InnoDB table space.
The system tablespace is the storage area for the
InnoDBdata dictionary, the double write buffer, the change buffer, and undo logs. It may also contain table and index data if tables are created in the system table space rather than file-per-table or general tablespaces.
The system tablespace can have one or more data files.
I mean the newly downloaded archive version, In the case of mysqld starts for the first time, is ibdata1 file still useful? even without it I can start mysqld without any problem and a new one will be generated.
I just want to know if this file must exists in the nonintall zip archive? For mysqld , when it starts for the first time, it seems this file is not essential and could be generated, so I think probably this file could be removed from nonintall zip archive.
Yes, the sever will create the ibdata1 if it does not exist. I am not sure which zip file you are using but the packager may have put it in there to a) save time, b) preload data (example databases), and/or c) just because it was there when they created the zip file.
If it really worries you then delete it.