The blockchain stores all the transactions, and groups them into blocks. Each block is linked(chained) together through hash functions.
That is why it is call blockchain.
Note that Satoshi Nakamoto does not use the term blockchain in his Bitcoin whitepaper at all. Blockchain is a term later given to the way Bitcoin transactions were being stored. This idea of linking data together through hash functions was first described in a paper from the early 90s. In fact this paper is one of Satoshi Nakamoto's sources he sites in his Bitcoin whitepaper.