If you are not aware about blockchain, this is what it means.

Formally, blockchain is a digital ledger technology (DLT), which focuses on recording and storing transactions of any type in a shared platform. A blockchain is, in the simplest of terms, a time-stamped series of immutable record of data that is managed by a cluster of computers not owned by any single entity. Each of these blocks of data (i.e. block) are secured and bound to each other using cryptographic principles (i.e. chain). Each block contains data involved in a specific transaction. As each transaction occurs, it is stored in a block and added to the chain. Together, the blocks form a distributed database that can hold a growing number of records—a blockchain.