locked vs encrypted bootloader

With all the uproar over the galaxy 3 bootloader, I do not understand the difference between these two types of bootloaders. I read the sticky regarding android bootloaders; however, that didn't really clarify the question at all. In fact, I have become more confused by various responses here and on xda devs.

I understand that certain bootloaders themselves are not encrypted but rather check the signatures on the boot.img, recovery.img, and system.img, and then proceed to load them if the signatures match, but I don't understand what type of bootloader this is. There seems to be more serious restrictions on certain types of bootloaders than others. Just wondering if anyone could clear up the confusion.