What Blockchain is constellation on?

Could you please clarify for me which blockchain the term "constellation" is referring to in this context? Is it a specific project or protocol built on a particular blockchain, or is it a metaphorical term used to describe a network of blockchains working together? If it's a specific project, could you tell me which blockchain it's built on and what its main purpose or features are? It would be helpful to have a bit more context to provide an accurate answer.