The Blockchain is a specific implementation of the distributed ledger technology (DLT) concept. It has received increasing attention since 2009 in form of the Bitcoin and its underlying Bitcoin Core Protocol. Basically, it is a virtual ledger within a network of computers, where every change is recorded and stored in a decentralized way .
The name of the technology refers to its data structure. Transactions are stored and cryptographically sealed in consecutive data blocks interlinked on basis of hash functions to prior data along a chain. This interconnection between blocks is one reason for a cryptographic immutability of transactions . Depending on access rights and the permission to validate transactions, three generic types of Blockchain Frameworks have been established in practice: Public Blockchains, Private Blockchains or Permissioned Blockchains. The Blockchain is the basis for cryptocurrencies such as Bitcoin or Ether, which are each based on a Public Blockchain.
 IHK Region Stuttgart
 Karzel, D., Klinger, P.
 Plazibat, A. (2019): The Business Potential of Distributed Ledger Technology
In General, the Blockchain is characterized by the following five features :
Distributed: Data on the Blockchain is sent decentralized to all nodes.
Unchangeable: If a block is appended to the Blockchain, it cannot be changed.
Transparent: The Blockchain is completely transparent for users who have access to the Blockchain.
Global Source of Trust: Nodes in the Blockchain can be sure that all other nodes see the same data after mining.
Programmable: Due to the unchangeability and traceability, contractual obligations can be represented as code.