A block is a fundamental component of a blockchain. It serves as a digital container that holds data about transactions, similar to a page in a ledger. Each block typically contains a list of transactions, a timestamp, a reference to the previous block, and a unique identifier called a hash.

When a block is filled with transaction data, it is added to the blockchain in a linear, chronological order. This addition is secured through a consensus mechanism, such as proof of work or proof of stake, which ensures that the data within the block is verified and immutable.

Each block strengthens the security of the entire chain, as altering information in one block would require changes to all subsequent blocks. This structure makes blockchain technology resistant to tampering and fraud.

Blocks work together to form a chain, creating a transparent and decentralized record of all transactions. This allows users to track their assets and enhances trust, as data is publicly accessible and verifiable on the blockchain.