A blockchain is a continuously expanding collection of documents, known as blocks, that are securely connected to one another using encryption.
Each block includes transaction information, a timestamp, and a cryptographic hash of the preceding block (generally represented as a Merkle tree, where data nodes are represented by leafs)
The timestamp demonstrates that the transaction data was present at the time the block was published in order to be included in its hash. Blocks create a chain because each one has information about the block before it, hence strengthening the links in the chain. Because once recorded, the data in any given block cannot be changed retrospectively without changing all following blocks, blockchains are resistant to data manipulation.