Blockchain technology was announced through the paper titled "Bitcoin: A Peer-to-Peer Electronic Cash System" by Satoshi Nakamoto in 2008. Interestingly, this paper does not specifically use the word "blockchain".
This paper talks about a "purely peer-to-peer version of electronic cash" where "the network timestamps transactions by hashing them into an ongoing chain of hash-based proof-of-work, forming a record that cannot be changed without redoing the proof-of-work".
PT-BSC defines the terms blockchain, distributed ledger system and hash function.
(a) blockchain
A blockchain is a peer-to-peer network which timestamps records by hashing them into an ongoing chain of hash-based proof-of-work, forming a record that cannot be changed without redoing the proof-of-work. A blockchain can be permissioned, permission-less or hybrid.
(b) distributed ledger system
A distributed ledger is a peer-to-peer network, which uses a defined consensus mechanism to prevent modification of an ordered series of time-stamped records. Consensus mechanisms include proof of stake and federated byzantine agreement.
(c) hash function
A hash function is an algorithm mapping or translation of one sequence of bits into another, generally smaller, set known as hash-result such that an electronic record yields the same hash-result every time the algorithm is executed with the same electronic record as its input making it computationally infeasible to (i) to derive or reconstruct the original electronic record from the hash result produced by the algorithm; (ii) that two electronic records can produce the same hash result using the algorithm. Adapted from section 3 of the Information Technology Act. Examples of hash functions include SHA-1 and SHA-2.
Note: Blockchains inherently involve multiple parties and organizations. In this document, the term organization includes, unless repugnant to the context, all participating organizations that have agreed on a common security framework, framework revision procedures, and security compliance monitoring processes.