A blockchain is a set of protocols and cryptographic methods that enable a network of computers to work together to securely record data within a shared open database.
This database consists of a series of encrypted blocks which contains the data. The blockchain is a continuously growing list of these blocks of data which are linked and secured using cryptography. This makes it a trusted database with this trust maintained by open secure computer code and encryption instead of any single institution.
Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree). The timestamp proves that the transaction data existed when the block was published in order to get into its hash.