What is "off-chain data"?

Off-chain data,' also known as real-world or external data, pertains to the existing global data infrastructure outside of the blockchain, which can be accessed by smart contract applications via oracles. Oracles to smart contracts are like the Internet to computers. Only when smart contracts are connected to real-world data through oracles do the scope and functionality of smart contracts significantly increase and improve. In the context of Bond Oracle, off-chain data principally refers to users' social graphs and behaviours within social networks.