The network of computers that maintain a blockchain is called a "node." Each node has a copy of the ledger and helps to verify new transactions by solving complex mathematical problems. Once a block of transactions is verified, it is added to the chain and becomes a permanent part of the ledger. One of the key features of a blockchain is that it is immutable, meaning that once a transaction is recorded in a block, it cannot be altered or deleted. This makes it a secure and transparent way to store and transfer digital assets. Blockchains are the technology behind cryptocurrencies like Bitcoin, but they can also be used for a wide range of other applications, such as supply chain management, voting systems, and digital identity.