Blockchain was conceptualised as a "chain of blocks" between 1982- 1992 which could be used to store and share document timestamps which could not be tampered with.
Formulation of bitcoin was one of the practical uses of blockchain technology.
Satoshi Nakamoto, the creator of bitcoin, borrowed the idea of blockchain with the difference that it would record monetary transactions.
So to put in simple terms, blockchain is a ledger of transactions. which is shared and replicated across various networks and can be updated without the need of a central authority.
Take the transactions to be bundles. And one such bundle is called a block which includes timestamp and other relevant data. These blocks are lined up chronologically (according to date and time), thus forming a "chain".