Blockchain is a digital ledger technology that allows for the creation of a decentralized and secure record of transactions. A blockchain is essentially a database that contains a constantly growing list of records, called blocks, that are linked and secured using cryptography.

Each block contains a set of transactions, and once a block is added to the blockchain, it cannot be altered or deleted. This makes the blockchain a secure and transparent way to record and verify transactions without the need for a centralized intermediary, such as a bank or government.

The most popular and well-known blockchain is the one that powers the cryptocurrency Bitcoin. It is called the Bitcoin blockchain and was created in 2009 by an unknown person or group of people using the pseudonym Satoshi Nakamoto.

However, since then, numerous other blockchains have been developed, including Ethereum, Ripple, Litecoin, and many others. Each blockchain has its own unique features and uses, and some have gained more popularity and adoption than others depending on the specific industry or application they target.

For example, Ethereum is popular for its ability to create decentralized applications (Dapps) and smart contracts, while Ripple is popular for its use in cross-border payments and financial services. The popularity of each blockchain can change over time as new use cases and applications are developed, and as the technology evolves.