I keep hearing people think that the “blood” in “blood elf” or “blood knight” refers to literal blood.
I have heard everything from them being vampires to them using blood “magic” as their source of power.
The term “blood elf” in warcraft three was explained in lore to refer to two things:
1a) in elf language, the word used for “elf” means child.
1b) in elf language, ALL royal high elves were called “blood elf” or “children of the blood” to refer to royal heritage.
2) after arthas destroyed the sunwell, the rapidly maddening kael’thas declared that ALL high elves would call themselves “children of the blood” because while their royal family was all murdered they are still of the same “master race” as their fallen kings.
“blood elf” was therefore (narrowly) used originally to refer to the royal family, and then widely to refer to a group of racial supremacist high elves who followed kael’thas after arthas blew up the sunwell. the name just stuck from there because it was the name they went with when they joined “the red worldwide superpower.”
“blood knight” refers to a fringe group of ex-spellbreakers and ex-priests who were corrupted by the sunwell exploding, and decided to be the vanguard of this new “communal royalty” of the “supreme people.” they captured a naa’ru and tried to use it to “power” their new order, then fashioned their order after human paladins for aesthetic purposes.
most of the blood elves ended up being the enemies you killed during the sunwell plateau war, which is why there are lore paintings of lady liadrin (the leader of the blood knights) tearing apart her blood knight tabard after putting on the “shattered sun” tabard as a sign that she abandoned her racial supremacy to try to be a real paladin. the shattered sun soldiers were a mix of draenei helping ex blood knights to be real paladins instead of the corrupt stormtroopers they were before; each of them broken, guilty, and looking for redemption in the light though unworthy of it.
once the sunwell plateau war ended, lady liadrin then renamed her half of the shattered sun as “blood knights” again; this time being the literal royal guard of the new king lor’themar.
none of them drink blood, none of them really have anything to do with blood (that I know of). so where did people get this idea from? maybe confuse them with the scourge elves in northrend who DO drink blood, as arthas’ direct insult against the entire blood elf race for opposing him and building themselves back up?
the whole blood elf / blood knight story arc in tbc is to show all the blood elves as irredeemable, corrupt addicts and mass murderers; who then try to be redeemed anyways and succeed.
the whole blood elf starter zone is full of degenerate nonsense and evil; so that when you get to ghostlands they smack face first into what arthas did, you start to realize that you might have just become just as evil as arthas in your attempt to get revenge against him.
then eventually everything about the blood elves is challenged throughout the story, and eventually all blood elves basically become (somewhat) high elves again after sunwell plateau.
this is never really told well in game, because of how zones do not change as you level up (therefore the blood elf starter areas never actually reform like they do in lore, and stay forever as scum), and ESPECIALLY because blood elves were made into a horde race (for real life business reasons) so their redemption has been soured by taking part in every atrocity azeroth has faced since tbc.
I think in lore, the blood elves mostly keep to themselves and are only allied with the horde for political reasons, with only a small part of their royal family (and therefore the blood knights) and a mercenary-staffed military apparatus (like a foreign legion) even having the slightest interaction with the horde. this is not at all reflected in game, because well over half the horde players are blood elves; and silvermoon might as well not exist outside of tbc.