These things could include: Population Density of various creatures / races, How good the economy of the world is, The amount of raw materials ( veins / trees / fish ), Historical Events that took place, etc.
Just for the sake of future questions that may arise to this post I'll go ahead and go into detail of how this could work.
How it works
So, upon creating a character you're given a question asking if you would like to change any of the aspects given. If you hit no, you're given the default settings ( the way the game should be ). If you hit yes, you're allowed to change certain things about the game.
Population Density Of Various Creatures / Races
One of the things you could change would be the population density of certain races + creatures. For example, you can increase the population of the Argonians and decrease the population of the Khajiit. Another example would be increasing the population of Mud Crabs and decreasing the population of Cliffracers ( if they're in the game ). Doing this would make it so you would find a ton of mud crabs along the coast, and very few Cliffracers along the cliffs.
The Economy
Another thing you could change would be the economy. What if you could control the density of the poor populations throughout the world. What if you could control the prices of various raw materials and such? Just another thought.
Raw Materials
Players would have the option to control the amount of raw materials throughout the world. You would be able to make all of the raw materials very abundant, or scarce. This could greatly effect the economy. This might not even be needed, it could just fit in with the economy option, but just an idea.
Historical Events
Players can determine the events that occurred previously in the game. I'm not very familiar with the lore, so I can't give any examples. But here's one for lolz: M'aiq the Liar manages to defeat Mankar Camoran and became Hero of Cyrodiil.
Basically I just took the idea from Bioware. In Dragon age 2, you could choose the historical events that took place in the previous game. In Mass Effect 2, you could choose your character's past.