# Blockchains A **Blockchain** is a type of database that is made up of a growing number of records, called blocks, that are linked together in a linear fashion. Each block contains a record of multiple transactions, and once data is recorded on the blockchain it cannot be altered. The blocks are added to the blockchain in a chronological order, and each block includes a cryptographic hash of the previous block, a timestamp, and transaction data. The [decentralized ](/glossary/definitions/decentralization.md)nature of the blockchain means that it is not controlled by any single entity, such as a government or financial institution. Instead, the network is maintained by a network of computers, known as nodes, that validate and store the transactions on the blockchain. This decentralized structure allows for a secure and transparent system for recording transactions, as every node on the network has a copy of the entire blockchain. One of the key features of the blockchain is its ability to create a secure and transparent system for recording transactions without the need for a central authority. Because the data on the blockchain is distributed across the entire network, it is virtually impossible for a single entity to manipulate the ledger. The use of cryptographic hashes and timestamping ensures that the data on the blockchain cannot be altered retroactively without the [distributed consensus](/glossary/definitions/decentralization/distributed-consensus.md) of the network. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.allforone.app/glossary/definitions/decentralization/blockchains.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.