A blockchain is a distributed ledger that records all transactions that occur on a network. The term decentralised is often used to describe a blockchain because all participants on the network have a copy of this ledger and work collaboratively in order to maintain it. It’s this concept of decentralisation that makes the blockchain a very powerful tool for businesses to incorporate into their existing infrastructure.
All information recorded to a blockchain is done so in an “append-only” fashion with the help of cryptographic hash functions. Such techniques make transactions added to the ledger immutable. By making a blockchain immutable serves as a system of proof to all participants on the network to ensure that whatever transaction was added to the ledger had not been modified thereafter.
Smart contracts provide controlled access to the ledger by participants of the network in order to help maintain and update it. These are functions that interact with the blockchain which are run automatically once a condition has been met. They also provide helpful functions such as the ability to query data on the ledger.
The ordering in which these transactions are approved and recorded to the ledger is the consensus. This process is vital as it allows for the ledger to maintain synchronicity across the network.