A Blockchain is a data structure in which the information contained is grouped into sets (blocks) to which meta information related to another block of the previous chain is added in a timeline, so that, thanks to cryptographic techniques, the information contained in a block can only be repudiated or edited by modifying all subsequent blocks.
This property allows its application in a distributed environment so that the blockchain data structure can act as a non-relational public database that contains an irrefutable historical information. In practice, it has allowed, thanks to asymmetric cryptography and summary or hash functions, the implementation of a distributed accounting register (ledger) that supports and guarantees the security of digital money.
Following an appropriate protocol for all the operations carried out on the blockchain, it is possible to reach a consensus on the integrity of your data by all the participants of the network without having to resort to a trusted entity that centralizes the information. Therefore it is considered a technology in which the "truth" (reliable state of the system) is built, achieved and strengthened by the members themselves.
Blockchain technology is especially suitable for scenarios in which it is required to store data in an orderly manner over time, without the possibility of modification or revision and whose confidence is intended to be distributed instead of residing in a certifying entity.
The blockchain is used as a non-modifiable public notary of the entire transaction system in order to avoid the problem that a digital asset can be spent twice.