TextureCube is a cube texture, often used to set the scene's skybox. The cube texture can be obtained by setting the panorama ImageAsset to the TextureCube type, or it can be generated in the Creator.
Set to Cube Mapping
After importing the ImageAsset into Creator, you can set it to texture cube type in the Inspector panel, and click the green checkbox in the upper right corner to save the changes.
Once set up, you can see in the Assets panel that a textureCube subresource has been created below the original image resource, along with the six textures that make up the TextureCube.
The TextureCube obtained by making a CubeMap in Creator is as follows:
For the specific use of TextureCube and how to make CubeMap, please refer to Skybox - Setting up CubeMap.