Noob Question: Are there multiple instances of the Ethereum Blockchain?

Nathan_Drake Azure Blockchain Service deploys a private or "permissioned" version of Ethereum called "Quorum"; only authorized members of your blockchain network can interact with the blockchain.

Also, each instance of a Quorum blockchain is private.

Note it only makes sense for you to use blockchain as a ledger if you have some need to share the records on the ledger with some outside parties. A blockchain is not much use within a single organization; its primary purpose is to enforce trust in transactions among affiliated but not necessarily fully trusted partners.