This is my table's game-world reference for Changeling: the Lost, a game system originally by White Wolf Publishing and now done by Onyx Path Publishing. Not all of my players own the book and so much information is recreated here, but all rights are reserved by the creators. Also, my table has certain homebrewed rules that allow our games to move along swiftly and so not all of the information is canonically correct and should not be relied upon by players not at my table. That being said, welcome to my world.
A Changeling is a person, more or less, or even better, a Changeling is what is left of a person when the True Fae have taken the person and dragged them through the Hedge that separates our world from theirs. Once there in the Fae Realm of Arcadia, or Faerie, the True Fae rip away the humanity of the captive and reshape them into whatever the Fae desires.
Every Changeling has a Seeming. This is what form the True Fae shaped them into, twisting and molding their flesh and spirit into a body suited to the Changeling's purpose. Every Changeling also has a Kith. This is whatever profession the Fae shaped them to do, breaking and reshaping the mind and spirit to make a Changeling perform a function for them. A Changeling with an Elemental Seeming and a Kith of Bright One may once have been a living candelabra in some Fae castle, like Lumiere from Beauty and the Beast. A Changeling who bears a Wizened Seeming may appear like Rumpelstiltskin for how they spin gold from straw. Or like Brownies crafting shoes. Or maybe that Ogre Gristlegrinder is just waiting for an Englishman, be he live or be he dead, so they can grind its bones to make the bread.
The Fae are very much creatures of stories and folklore, and they turn mortals into lesser characters in the stories they spend forever playing out. But some of these poor, unfortunate souls escape their torments, their durance. Those are Changelings.
They flee their captors and run through the Hedge, building a new identity, a Mask that they hide over their true selves, out of the ripped away bits of others taken by the Fae and whatever of themselves they could hold on to. They take what their Fae Keepers made them into, and whatever they were made to do, and use those skills to escape.
The True Fae will always search for their lost property, and often send their Huntsmen to find what is Lost. But Changelings are smart, banding together to withstand the Huntsmen and their Wild Hunt. They form small groups called Motleys. Motleys band together to form large groups called Freeholds that are governed by some manner of Court system.
Motleys are a support system for Changelings and kind of a found-family that helps the Changeling rebuild some semblance of a life. They help each other out and support each other's goals. Motleys are a tight-knit band, usually. But a Huntsman might tear through a Motley, and so reinforcement is needed. That is where the Freehold stands.
Every Freehold is a settlement that has Changelings. It is built by Changelings and maintained by Changelings for Changelings. It is community and safety in numbers and is governed by the predictable changes of something in the world that Changelings have no control over, like seasons or the Moon or the Night/Day cycle. This way power cycles through the courts that each represent their part of the cycle. After all, everybody wants to rule the world.