A blockchain is a type of distributed ledger comprised of digitally recorded data in packages called blocks.
These digitally recorded "blocks" of data are stored in a linear chain. Each block in the chain contains data (for example, a bitcoin transaction), which is cryptographically hashed. The blocks of hashed data draw upon the previous block of data in the chain, ensuring all data in the overall "chain of blocks" has not been tampered with and remains unchanged.
A blockchain is just one type of distributed ledger. Not all distributed ledgers necessarily employ blocks or a sequential chain of transactions.
Although the term “blockchain” is used more frequently than “distributed ledger”, a blockchain is only one of the many types of data structures that provide secure and valid achievement of distributed consensus. The Bitcoin blockchain, which uses “Proof-of-Work” mining, is the most publicly proven method used to achieve distributed consensus. However, other forms of distributed ledger consensus exist such as Ethereum, Ripple, Hyperledger, MultiChain, and other private enterprise solutions.