What is a blockchain? In simpleton terms..
In simpleton terms? A "blockchain" is a chain of blocks.
To get a bit more complex, it is a crypto-currency transaction ledger.
The "blocks" are collections of transactions that are added to the database together all at the same time. Each block of transactions has a header (some information before the transactions are listed) with important details about the data in the block, as well as information that qualifies the block to be added to the database. One of the pieces of information in the header is an identifier that uniquely identifies the previous block added. In this way there is a "chain" of blocks each identifying the previous block all the way back to the first block.
