I'm working on Samsung Galaxy Tab tablets, specifically with Tab 3 (SM-T210) and Tab 4 (SM-T230), and being learning a bit about the boot and recovery images and the bootloader. I have not being able to find the answer to this very simple question: Is Download Mode Samsung's Bootloader? If not what is the difference?
Yes and no. The Download Mode is an interface between the Loke component, which resides in the bootloader, and Odin/Heimdall. In fact, if you issue the reboot bootloader from your device's command line, it will boot the Download Mode. (thanks to @death-mask-salesman)