A chain in cryptocurrency refers to a sequence of data blocks that contain information about transactions. Each block in the chain is linked to the previous one, forming a continuous and secure record of all transactions that have taken place. This chain is decentralized and distributed across multiple computers or nodes in a network, making it highly secure and resistant to fraud or tampering.

The chain is maintained by a consensus mechanism, which ensures that all nodes in the network agree on the validity of transactions and the order in which they are recorded. This consensus mechanism typically involves a process known as mining, where nodes compete to solve complex mathematical problems in order to add new blocks to the chain.

The chain serves as the backbone of the cryptocurrency system, providing transparency and accountability for all transactions. It also allows for the creation of new coins through a process known as mining rewards, incentivizing participants to contribute to the security and integrity of the network.