Blockchain is the underlying technology that makes cryptocurrency possible. Blockchain is a digital ledger of transactions that can be used to facilitate secure, anonymous, and peer-to-peer exchanges. It is essentially a public database of entries that are secured and linked together by cryptography.
Cryptocurrency, on the other hand, is a form of digital currency based on blockchain technology. Cryptocurrencies are digital coins created and controlled by encryption techniques in order to facilitate secure, anonymous and decentralized transactions. They are often considered to be an alternative currency to fiat currencies such as the US dollar or Euro, although their stability and value have been a source of considerable debate.