Such a nice question I must say. I just hope my answer will be able to help a little.

I have met people who have zero knowledge about Blockchain and with my explanation many understand what a blockchain is.

In a bit to explain it to somebody who has zero knowledge about cryptocurrency and blockchain, I run faster to using the Bank as a case study. Now, this is how I explained it to them.

I go ahead to explain that Blockchain is just like your local bank. Imaging Blockchain as the structures, by structures, I mean the building where different bank related activities is been carried out. All activities in the bank is been stored in their database this same thing is applied to Blockchain. In Blockchain all your activities is been recorded in their database. Bank is the opposite of Blockchain. By opposite, I mean that the Bank is a physical structure while Blockchain is a coded structure that is build online i.e it is not a physical structure.

Just like in a bank, you can swap your local currency to any other currency, same thing can be done using the blockchain. Your different currency can be swap to any token.

Just like you have money like dollar, naira, pounds and so many currency in the bank, you have cryptocurrency in blockchain. The Cryptocurtency ranges from different money to the other. You have popular cryptocurrency like Bitcoin, Ethereum, hive, steem, litecoin, Uniswap, Eos, etc all in the blockchain, samething like having Dollar, naira, pounds etc

Now, how is this Blockchain better than our local. In blockchain, you can buy any Cryptocurrency without needing to leave the comfort of your home. You can easily sent token and receive token with ease without visiting your local bank. If the money hasn't delivered in your list of asset, you can easily check the transaction to ascertain if the person send it or not. But in case of bank, you will need to visit bank or call their customer care line to help you check the transaction status.

In blockchain, you can trade your token for additional gains, unlike bank. Although their is also the negative side. You have to have trading knowledge. While using the blockchain, just buying a coin and holding it can see you making good reward without you even engaging in any activities. This happens if the coin rises in value. You can still make loss just holding a coin if it drops in value too. This can't be done in banks except maybe you open a fixed deposit account and freezes your money for a particular time frame. You don't need to freeze your token before you can make good gain in blockchain.

With this few point of mine, I think I am able to explain what blockchain is in a lane terms.