A blockchain is a digitized, decentralized, public type of distributed ledger of all cryptocurrency transactions that is shared among a distributed network of computers. It is composed of a series of records, also known as blocks, which are connected and linked using cryptography to allow participants on the network to record transactions on the ledger in a secure way and without the need of an approval from a third party.

To make it simple, bitcoin technology works in such a way that a network of computers keeps a record of all the transactions made by internet users who transfer a unique piece of digital property or currency to another internet user, wherein the transfer is guaranteed to be safe and secure, everyone is aware about the transfer, and modification is not allowed.

As a distributed ledger, a blockchain is usually managed by a peer-to-peer network altogether complying to an agreement for verifying new blocks.

Blockchains are designed to be secure as it is a distributed computing system with high Byzantine fault tolerance, the capability of a computer system to resist failure from faulty components from reaching a necessary consensus. Because of this, blockchain has achieved a decentralized consensus which makes it suitable for recording data such as medical records and events and other records management activities. Part of its security methods is using public-key cryptography wherein value tokens that are sent across the network are documented as belonging to the public key, an address on the blockchain that is composed of a long string of numbers. When a blockchain is divided into two separate chains as a consequence of using two distinct sets of rules to govern the system, the situation is known as a hard fork.

Open blockchains are more user-friendly and convenient to use compared to traditional ownership records but they still require physical access to view. A permissionless, open, or public blockchain network does not require access control which means that new applications can be added to the network without any approval using blockchain as a transport layer. Cryptocurrencies such as bitcoin secure their blockchain by requiring new entries to include a proof of work. Although early blockchains were permissionless, permission or private blockchains who use access control over who gets access to the network are now existing.