A sky continent, also called an aerial continent, is a massive artificial structure that resides in a planet's atmosphere, usually the size of a large city or even a mountain range.
Sky continents are built for various reasons, most commonly to ease crowding issues on planets covered in cityscape. They are also a standard feature on inhabited gas giants, as well as terrestrial planets whose surfaces are too hostile to support life.
These monstrosities typically come in two flavors: a solid shell filled with city, or a platform upon (or beneath) which city is built. The framework is made from lightweight metamaterials, some of which naturally repel gravity or otherwise ease the burden on the primary antigravity systems.