What is Blockchain?

Blockchain is a data storage technology, which differs from classic database in several properties and very interesting structure.   

Blockchain can be imagined as a book of transactions, which is transparent and accessible to all its users. Another important feature of blockchain is the following: once any information is entered into the blockchain, it is impossible to change. Blockchain is a chain of blocks, where each block contains specific data, as well as a reference to the previous block