What does the ROM files (FACTORYFS, HIDDEN, CACHE, PARAM, etc.) mean?

From [INFO] What the ROM files mean

boot.bin This is the Primitive Bootloader. Seems to make some basic
initializations and finally loads the secondary bootloader.

Sbl.bin The Secondary Bootloader. It loads the PIT, the Linux kernel,
params.lfs and the modem. It also is responsible when the device is
charging while it's off. This file contains the picture you see when
in Download-mode. So it's also responsible for the flashing stuff and
getting into recovery.

The Sbl.bin seems to be there twice. The second one may be for backup,
if something bad's going on.

param.lfs A collection of JPEGs. These include the Galaxy S-Logo you
see first when booting the phone as well as the phone-!-computer
picture, the loading spinner and some pictures of an Android giving
some information: "CP CRASH UPLOAD MODE", "FORCED UPLOAD by KEY
PRESSING", "POWER RESET or UNKNOWN UPLOAD MODE", "USER FAULT Not
KERNEL PANIC UPLOAD MODE" and "KERNEL PANIC UPLOAD MODE". And there is
the Logo of NTT docomo, which is a Japanese mobile operator company.

Maybe there are more information in this file, but I didn't extract
it.

The rest of the files should be rather obvious:

zImage is the Linux kernel.

recovery Backup Kernel. Don't know if it's
used on every device.

factoryfs.rfs is the System partition with the
Android system.

dbdata.rfs is the partition where the app data get
stored.

cache.rfs is for Dalvik cache.

modem.bin is the Modem.

From How to Use Heimdall – specifically on Samsung Captivate – Download 512 513 and 803 PIT files

• IBL+PBL is the boot loader, be extra careful with it;


• PIT is the partition table;


• EFS contains some important data like IEMEI, be extra careful with it;


• SBL is the second boot loader;


• SBL2 is the backup of the second boot loader;


• PARAM contains some images used as various stage of the boot process;


• KERNEL is the kernel;


• RECOVERY is the backup of the kernel;


• FACTORYFS contains /system file system which is some kind of root file system;


• DBDATA contains /data file system which is the database to store application parameters;


• CACHE contains /cache file system which contains the Dalvik cache;


• MODEM contains the firmware for the modem.