Legacy BIOS is the old standard of pre-boot for computers. BIOS = Basic Input/Ouput System, is what's on all computers before UEFI came out. UEFI is different from BIOS, so to differentiate them one is referred to as "legacy BIOS" and the other is referred to as UEFI.
SLIC is an acronym that just stands for "Software Licensing" that refers to how they do licensing for OEM systems in reference to "built-in" keys:
https://msdn.microsoft.com/en-us/library/windows/hardware/Dn653305(v=VS.85).aspx
That's what I'm kinda waiting for - though I guess I don't really have much reason to anymore since my DreamSpark copy of Win8.1 is technically a retail copy so I should be able to transfer it to a new system if I upgrade (my biggest concern). Though I may way a bit to see if that is indeed the case. Either way, hopefully I'll get a vanilla Win10 license from DreamSpark as well. I'll have to check my work MSDN account to see if there's one available there yet.