A supercritical fluid is any substance when at a certain temperatrue and pressure reaches above it's critical point, where the distinct seperation between the liquid and gas phases do not exist, but below the pressure required to compress it to solid. It effuses through proous solids like gas does overcoming the mass transfer limitations that slow liquid transprort through such materials. They are one of the only forms of liquid that can be found in the connection-roads, however the properties are a little different than how they are inside Worlds. In the connection-roads it visually settles down into a puddle and is comprised of mostly h2O and some other vague minerals. The actual supercritical fluid part of it rests only visible in red light, generally not requiring any conditions similar to ones found on Worlds like temperature.
Connection-Fluid comprises a vast majority of the connection-crossroads but not the entirety, there is a hypothetical blackrock wall that encapsulates all the connection-fluid that lay across the meridian. Nobody has been able to set sail in the connection-fluid sea however. When redlight is shone on the fluid a large beam of mosaic smoke shoots up indefinitely towards the sky, it's theorized all of the mosaic smoke conjoins past the connection-clouds to a vast network blamed for "Background Static".
Connection-Fluid is used in Black-Boxes, Batteries, Hyper-Flashlights, and currency. When solidified it is turned into currency.