Magical Underpinnings of Reality

In Fantasy settings magic and the mythic creatures are not abnormal, but a natural part of the world. It's normal to see wizards, the Anthropomorphic Personification of love, and even weirder fare sit down every third tuesday for tea and biscuits (baked by tree elves, of course). Many things that are explained by physics in Real Life may even have completely different explanations in this world, such as The Grim Reaper going about ending lives (not necessarily killing, mind you), that fires are actually small (or enormous) imp-like beings, or that there are Nature Spirits that guide nature.

Then there's settings that take it Up to Eleven. In a world where there are Magical Underpinnings of Reality, everything that happens in the world is attributable to a magical force, worker, artifact, or another explanation. Gravity? There's a gigantic god who is holding the world like a bucket and spinning to create centrifugal force. The stars? They're cute little lightbulb girls that are suspended on a gigantic scaffold. The changing of the seasons? The Fair Folk go about telling the plants to grow, bloom, or sleep. The sun? It's a giant lamp fueled by the laughter of good children, which is gathered by angels, so be good or the sun won't shine!

In short, most or even all the natural world works thanks to magical means. In a weird twist, they may even use industrial or scientific methods like worker shifts of gnomes who paint the leaves for fall, or machines that manufacture clouds. If this doesn't jive with science as we know it, there may be a Masquerade, or the magical aspect is only obvious in the Magic Land or Spirit World dimension parallel to the mundane world, but is no less important to the natural world. Some stories have the Magical Underpinnings of Reality act as Cosmic Keystones to the real world counterparts, so kidnapping the Maiden of Spring effectively stops spring from happening in the real world as well.

Essentially, everyone paints frost on the windows.

Compare Fantasy Kitchen Sink. See also Planet Eris. Can be the result of enough Odd Job Gods. To populate this world usually requires authors make liberal use of Crossover Cosmology.

Examples of Magical Underpinnings of Reality include:

Film

In Nocturna, the nighttime world invisible to humans, fey beings go about ensuring that everything necessary for a normal (not necessarily "good") night's sleep happens. There's a writing department for dreams (and a cadre of tiny women who deliver and read them to you as you sleep), hair mussers that mess up your hair as you sleep, "composers" of nighttime sounds, and all lights are actually living beings. Stars are immortal doll-like lightbulb women who are suspended from a giant scaffold held aloft by a lighthouse; street lights are firefly-like workers in mining gear.
In Stardust, stars in our world are the typical giant balls of gas (or meteorite), but on the other side of the wall they are immortal women who float in the sky and shine at night (unless someone hits them and knocks them down). A star crossing the wall turns into a lump of rock and metal.
In The Magical Legend of the Leprechauns, Trooping Fairies run nature worldwide, they manufacture leaves, make sure snow and spring and rain all take their due course, etc. But a war with the leprechauns distracts them from their duties, and so natural weather patterns worldwide collapse into chaos.

Live Action TV

Charmed is loaded with this trope to the nth degree.

Literature

Tom Holt's novel Here Comes The Sun is about a group of grumpy and bureaucratic beings responsible for ensuring the sun rises and the Nile delta floods and so on.
In The Dresden Files the conflict between the Summer and Winter Courts of the Sidhe have a major impact on the change of the seasons and the overall climate of the planet. Global Warming is attributed to Summer having a slight advantage over the last few decades.
In The Kingkiller Chronicle, the moon disappearing from the sky isn't caused by the moon being between the sun and the Earth, it's because when it's not in the sky, the moon is actually elsewhere, serving as the moon of Fae. This phenomenon may have been caused when a boy named Jax (Actually Iax, a long dead Namer, and purportedly the greatest of them all at the time.) learned the moon's name and partially trapped it in a box, hence the Just-So Story of why the moon waxes and wanes.
In the Mune Shinri (which the video game Oracle of Tao is loosely based on), reality is run by scientific laws, as much of the empirical world accepts. But behind thoses laws, the people keeping them working are various spirits, and a group of beings called Reapers.

Tabletop Gaming

This is how Mythic Reality works in Nobilis. Everything has an anthropomorphic spirit. Everything. Your car, the chair you're sitting in, your teeth, etc. Mythic Reality is not "how things really work" so much as an alternative way of understanding the universe to "Prosaic Reality," the world of bound by laws of physics that we normally perceive.
- However, Earth is the only world on the Tree which has a Prosaic Reality. Mythic Reality is the default everywhere else.
- Being made forcibly aware of these magical underpinnings tends to drive mortals insane -- Earth itself couldn't deal with the knowledge of a world in which the capricious whim of a god can wipe out the dominant lifeforms on the planet or transport rabbits from their peaceful undersea homes to the world of land, so it's not surprising that mere mortals can't, either. In 3e, the Locust Court allows victims to forget this knowledge and regain their sanity, if they can find it. Otherwise, those who can't learn to cope with the knowledge on their own are basically doomed to living with a view of the world that's accurate, but not rational or functional, and which causes them to (rightly) be considered insane by their peers.
Exalted has everything -- everything—in Creation made out of Essence, to the point that motonic theory (referring to "motes," the basic unit of Essence) is the setting's equivalent of atomic theory. Sorcery is the setting's equivalent of understanding physics to the point where you can tell them to sit down and shut up. In addition to that, everything in reality, from a single grain of rice to the sun itself, has a god that represents it. Causality is entirely dependent on the Pattern Spiders weaving the Loom of Fate properly.
- Unusually for this trope, the Magical Underpinnings Of Reality take up a managerial role. If you kill or traumatize the god of a river—which, as an Exalt, is pretty easy and usually exactly the wrong thing to do—the river won't disappear or dry up, but it will suddenly become far less predictable.
Changeling: The Lost has it so that this is how Arcadia works. Every thing is a sentient force that requires you to make a Contract with it in order to gain its benefits. For instance, you need to make a Contract with Water in order to quench your thirst, though it can still drown you even if you haven't signed on. The Gentry gain most of their magic by forging these Contracts with the forces that technically hold the keys, and their changeling servants gain mastery of them by proxy.

Video Games

Oracle of Tao has the entire universe operate not through faeries, but through mechanistic laws (for instance, fire magic runs on principles of thermodynamics, meteorological principles for thunder and cold magic, et cetera). The Dark World works also works, but on entropy rather than energy. But the reverse is true, that everything from electricity to magnetism relies on faith, strong will, or emotions. This would all be normal, except mundane things like cellphones and ATM machines also run on magic, and the former can literally call God.
In ZanZarah, everything in the eponymous Another Dimension is powered by faeries (small magical mostly non-sentient creatures): stone faeries hold mountains together, nature ones make trees grow, water ones keep rivers flowing, etc., etc.

Web Comics

Gunnerkrigg Court has the Moddey-Dhoo mentioning that Psychopomps' "clients" ensure that "the world continues to spin", though didn't clarify beyond this.

Western Animation

My Little Pony Friendship Is Magic: The ponies on that world do everything - wrap up the winter, wake up the animals, move the clouds to make rain, produce the rainbows and snow, make the autumn leaves fall - and their God Empresses are responsible for raising the sun, the moon, and the stars in general. In fact, the Everfree Forest is considered an unnatural site precisely because nature takes care of itself there.