For busy managers : what is a blockchain ? (explained in 5s)
I was challenged by a friend to explain the blockchain in 5 seconds. Here is my attempt.

The blockchain is the technology behind the cryptocurrencies like Bitcoin.

To simplify, you can consider a blockchain as a shared excel file. Anybody can read it and add a new row at the end of the sheet but you cannot modify or suppress the existing data. In order to insert a row, there's a catch, you need to solve a puzzle.