The term blockchain refers to a decentralized ledger in which transactions are recorded in an immutable ledger that is accessible by anyone participating on the network or through a public blockchain explorer application.  

An analogy to blockchain technology would be an extensive database replicated on multiple computers around the world, which is continuously synchronized and verified by the network’s consensus protocol. There isn’t a single centralized authority for this data that could allow the data to be compromised. Additionally, through the blockchain explorer, all transactions can be audited by anyone. This technology has opened the door for many novel applications and business models that previously had to rely on trusted intermediaries or centralized sources of truth. 

Cryptocurrencies, such as Bitcoin, are digital currencies based on blockchain technology where economic transactions are recorded and verified by consensus by all of the nodes participating on the network. 

Other projects such as Ethereum are used to create Smart Contracts that allow multiple parties to have a trusted, verifiable, agreement recorded on the blockchain. Additionally, these contracts have the ability to dynamically execute contract clauses based on programmable criteria. 

For more information on Bitcoin and the origins of Blockchain, please read the founding white paper written by Satoshi Nakamoto.