Certain questions and discussions tend to get repeated every other day on TES lore boards, so I decided to keep a collection of those topics.
Since this thread is supposed to be purely informative, no discussion shall be held. Feel free to message me if you think something should be added or edited, though.
I want to learn more about Elder Scrolls lore. Where should I start?
The best way to get to know the lore of the Elder Scrolls series is to follow this handy guide over at the official lore forums. I also strongly suggest lurking regularly on that forum. TES offers many layers of lore, from simple historical dates to complex metaphysics and philosophy. It is not easy to get into, and at the beginning you won't understand most of the things said by lore buffs, but after a while, things will fall into place.
There's a great compilation of ESO lore questions and answers by @Lady Nerevar over at The Imperial Library http://www.imperial-library.info/content/elder-scrolls-online-lore-answers
Never consult the wikia on lore matters. It is rubbish, as proven here TES wiki or UESP wiki, which one is more reliable lore-wise?
What's a "Mer"?
Dunmer? Betmer? Bosmer? For someone who is new to the Elder Scrolls universe, these words don't make sense. They are names of races in the language of the Ehlnofey, the original ancestors of man and elves. While mer technically means "folk", it is mostly used as an alternative word for elves.
The Aldmer, the Old Folk, were the first elven race to live on Nirn.
The Altmer, or High Folk, are the elven race least removed from the Aldmer. They take great pride in their almost-purity.
The Bosmer, or Wood Folk, are the smallest of the merish races. They hail from the Valenwood forest, and are bound by the Green Pact tonot let anyone harm their forst's plants. That includes eating the fruits or using the wood. Breaking the Green pact would probably mean the end of the Bosmeri race.
The Dwemer, or Deep Folk, are often mislabeled as dwarfs, even though they weren't small and stout at all. They lived underground and built sophisticated automatons. They mysteriously vanished in the first era.
The Dunmer, or Dark Folk, began as a religious sect of Altmer or Aldmer. They fled prosecution and lived as nomadic tribes in the ash wastes of Morrowind. Their grey skin and red eyes are the result of a curse laid upon them by the Daedric Prince Azura after Indoril Nerevar, who unified the tribes, was murdered by his trusted advisors. Nerevar was against using the Heart of Lorkhan to attain divinity. With him out of the way, they became what is now known as the Tribunal, the rulers and gods of the Dunmer. The average Dunmer believes that nerevar was killed by the traitor Voryn Dagoth and that the changes in skin and eye color were a blessing to mark the people favored by the gods.
The Orsimer, or Pariah Folk, are more commonly called orcs. They once were the followers of the Aldmeri god Trinimac and changed when Trinimac was devoured by the Daedric Prince Boethiah. The orcs nowadays are known as primitive savages, mostly because whenever they try to become anything more civilized or sophisticated, the Bretons and Redguards band together to throw them back into savagery.
Manmer - Man Folk - is a term seldomly used for Bretons, due to their even heritage.
Betmer - Beast Folk - is an umbrella term sometimes used for Khajiit, Argonians, Imga and other animal-like races. It is misleading, though, because it indicates relation where none exists. It could also be seen as a racist term.
What are the lifespans of the races?
This is a question that pops up ever so often, and there simply is no answer. We just don't know.
Dark elves are said to be able to live up to 1.000 years, though many die earlier because of the environemnt they live in.
Orcs have very short life spans and try to die in combat before they get old anyway.
Uriel Septim VII was 87 years old when he was assassinated. Since he was an emperor, we can assume that he would have lived quite a bit longer than ordinary Imperials.
Bretons might have marginally longer life spans than Imperials or Nords due to their merish heritage.
ZOS has partially answered this questionin an AUA, defying established lore as usual:
Elves live two to three times as long as humans and the “beast-races” (Orcs, Khajiiti, Argonians). A 200-year-old Elf is old; a 300-year-old Elf is very, very old indeed. Anyone older than that has prolonged his or her lifespan through powerful magic.
Are Khajiit werecreatures?
Many people have noticed that Khajiit have different forms which are dependant on the moon phases and that werecreatures tend to undergo transformation during a full moon. There seems to be a connection.
Werecreatures are people cursed (or blessed, depending on your point of view) by Hircine, the Daedric Prince of the Hunt. There are many kinds of werecreatures (wolves, bears, sharks, lions etc.), all people twisted by Hircine into perfect hunters. Why the transformation is triggered by the moons is either unknown or buried deep in the official lore forums.
Khajiit, on the other hand, have no connection to Hircine other than that he is one of many gods in their pantheon. Their form isn't violently changed every other night, it is determined by the moon phase they were born in. According to the Khajiiti creation myth, it was Azura who bound them to the moons because as Lorkhaj had protected Fadomay, the mother of all gods, so the Khajiit were to protect Nirni, the mother of all mortals.
Something TALOS something
ESO takes place in the yera 583 of the second era. Tiber Septim/Talos won't be born for almost 250 years. Thus, the nine divines are eight, there is no currency called "septimes," and no one has outlawed the worship of a god no one knows about.
All elves are nazis!
Most of us had the pleasure of encountering the Thalmor in TES V: Skyrim. Bethesda did their best to style them as the unarguable bad guys.
The Altmer have always viewed the mortal world as a prison. They want it to end so that every soul - merish, manish or other - currently trapped in the cycle of rebirth could return to their original state of divinity they have been robbed of by Lorkhan's creation of the mortal world. To reach that goal, the Thalmor wants to unmake everything that stabilizes the world. Talos, as the reborn Lorkhan (reborn is wrong, but the real explanation is a bit too complex for this), is one of the main obstacles the Thalmor have to face, and humans are the unwitting pawns of the devil - for that is what the Thalmor see in Lorkhan and Talos.
The point is, though, that the Thalmor as we know it from Skyrim won't be around for another 600 years. There is no elven supremacy movement yet - at least none with actual power.
And even in the time in which Skyrim is set, not all elves share the Thalmor's point of view. The Dunmer dont sympathize with them at all, and some High Elves have openly opposed the Thalmor.
What happened to the Dwemer?
Through the information provided by several quests from Morrowind as well as a good amount of discussion and speculation, we do know what the Dwemer were up to and how it could have ended. We won't know the ultimate answer until someone tells us, though.
Read this Imperial Library article for detailed information.