“Blockchain” doesn’t exist because it cannot be defined. Ask 10 people and you will get 10 different definitions. It’s a lot of fun, try it with people around you. It shows that it’s often wishful thinking: people call “blockchain” what they want it to be.
|A blockchain is a digital database containing information (such as records of financial transactions) that can be simultaneously used and shared within a large decentralized, publicly accessible network||Merriam Webster||A blockchain is not exactly a database, rather a log or audit trail (note: bitcoin uses a non-relational database library called LevelDB). I like the “publicly accessible” which excludes private systems, but it’s not clear what “used” and “decentralized” mean. Removing “such as” would make the definition more accurate.|
|“Blockchain” means a digital ledger or database which is chronological, consensus based, decentralized and mathematically verified in nature||Wyoming Law||I like the mention of “chronological” as timestamping is key indeed. However, a blockchain is not exactly a database (see previous definition). More importantly, it’s not clear what “decentralized” means.|
|Blockchain is a transparent and tamper-proof digital ledger||IBM||Idiotic. An SQL database can be made tamper proof and transparent.|
|Blockchain is an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way||Marco Iansiti & Karim R. Lakhani (HBR article, 2017)||By design, a blockchain is not efficient compared to a conventional system. “Quasi” permanence is a requirement, not a property. And it’s missing the core attribute of a blockchain: it works without a central authority.|
|“Blockchain” applies to a family of solutions that are inspired by parts of Bitcoin or similar crypto networks to solve business problems in a less centralized model||S. Taylor (twitter)||With this definition, the term “blockchain” retroactively applies to 30y+ old systems. If everything is a blockchain, nothing is.|
|A block chain is a linked list that is built with hash pointers instead of pointers||“Bitcoin and Cryptocurrency Technologies” by Arvind Narayanan, Joseph Bonneau, Edward Felten, Andrew Miller, Steven Goldfeder||It looks like the most accurate definition from a literal and technical perspective. But such a chain has no interest by itself. That definition doesn’t describe accurately the innovation that was bitcoin in 2009, nor the properties and benefits brought by the systems commonly called “blockchains“.|
|A blockchain is a ledger in which agents known as writers (or nodes) take turns recording information||Blockchain Economics Joseph Abadi and Markus Brunnermeier||If you think about it, it’s the most elegant and accurate definition of the list. A blockchain is about actually distributing the data “write” access right. The only issue: it focuses on the execution and doesn’t say anything about who decides on the changes to the system.|
If we call “blockchain” the innovation brought by bitcoin in 2009, IMO the closest definition goes like this:
a blockchain, or a distributed ledger, designates a system of record that is not controlled by a single entity or small group of entities, both at the design level and at the execution level.
The only blockchains implemented so far allow to exchange scarce digital units of value between unidentified people. Said differently: the only blockchains implemented so far are unregulated cryptocurrencies. More details why here.
Everything else that people call “blockchain”, I call “applied cryptography” or “software using cryptography”. What people wrongly call “blockchain” can still be useful, even though it’s not actually a blockchain, just because software is usually useful, and cryptography too.