Don't be spooked by the technobabble that people use to describe "blockchain." A blockchain is just a database. It isn't a particularly sophisticated one, either - you could create it in a spreadsheet with minimal effort.
There are some peculiarities with these databases. The first is that blockchains are append-only. That means that you can only add information - you can't just click on a cell and delete stuff that you've already added, or change it in any way.
The second is that each entry (called a block
) in the database is cryptographically linked to the last entry. In plain English, each new entry must contain a sort of digital fingerprint (hash
) of the last one.
And that's it! Since each fingerprint points back to the last one, you end up with a chain of blocks. Or - as the cool kids like to call it - a blockchain.
A blockchain is immutable: if you change a block, it changes the fingerprint. And since that fingerprint is included in the next block, the next block is changed too. And since that block's fingerprint... well, you get the idea. You end up with a domino effect where any change becomes evident. You can't alter any information without everyone noticing.