Blockchain

A blockchain is a distributed ledger that connects a decentralized network on which users can send transactions and build applications without the need for a central authority or server. It is a continuously growing list of records, called blocks, which are linked and secured using cryptography. As of 2022, there are more than 10,000 active cryptocurrencies based on blockchain, with several hundred more non-cryptocurrency blockchains.

Early Beginnings & Bitcoin Development
The first work on a cryptographically secured chain of blocks was described in 1991 by Stuart Haber and W. Scott Stornetta. In 1992, Bayer, Haber, and Stornetta incorporated Merkle trees into the blockchain as an efficiency improvement to be able to collect several documents into one block. In 1993, Proof-of-Work (PoW) mechanism was proposed to protect against spam and other network failures.