Come up with a non-technical minimalistic Blockchain definition [community engagement]

Hi Steemit Community,

everybody is talking about it and if you have a technical background, you will have no problem in understanding what a Blockchain really is. I am trying to come up with a minimalistic definition of the "Blockchain" term that everybody is able to understand - my non-technical grandparents as well as anybody that hasn't ever heard of Bitcoin, Cryptocurrencies, distributed databases, hashing, merkle trees, etc. But all my efforts resulted in a minute-long explanation of the datastructures, what digital currencies are and the different aspects of using a blockchain.

Tech-savy short definition:

For people with a technical background I'm using a very short definiton that sums it up pretty well, although you most likely will need to outline the term trustable afterwards. But that is a good entry point for further discussions in a real life setting.

The Blockchain is a trustable distributed database

[Task] Non-technical short definition:

You can find a vast amount of newspaper articles that deal about the Blockchain, but all of them fail to deliver the core message, what a Blockchain is in a few words. Can you do better?

Can you come up with a Blockchain defintion (as short as possible) so that also your grandma would be able to understand it?

I am aware that a short definition is by far not as accurate as a blog article or even a whole book about this topic. But that is not the goal. Keep in mind, to communicate the underlying idea efficiently and do not fall into the habit of being over-precise here.

Thanks for your kind support and ideas on this topic!