Trying to understand the options in TWRP backup

Question

This is a screenshot of the twrp screen after you choose "Backup":

I have the following questions:

1. What is the difference between the options "Boot, System and Data" on one hand, and "System Image" on the other?
2. Is the "Data" option for data of system apps and user apps, or only system apps?
3. I want to take a backup so that I can get a file that I can flash with Odin (that is, without requiring twrp). Which option should I use?
4. What is "Vendor Image", and how does it differ from "System Image"?
5. What is the difference between "Vendor" and "Vendor Image"?

Answer 1

1. as Irfan pointed out in his comment, "Image" means creating a partition image (using dd). Normally, TWRP creates tar archives with all the files located on a given partition, which then is much smaller.
2. "Data" contains all data – i.e. data & configuration from system apps as well as user apps. As the /system partition is mounted read-only during normal operation, that's where all "variable data" go (apart from files you store to the SD card).
3. Probably none of those. It's unlikely Odin understands any of the TWRP backups (you can try, and I stand corrected if you find out it can – but no guarantees from my side, including that it doesn't "brick" your device – I'm not a Samsung user)
4. Vendor is stuff very specific to your device provided by the "vendor", i.e. usually the manufacturer (including customizations) – while System is the "Android base" (though this separation is rarely absolute)
5. Same as between "System" and "System Image" (see 1.)