What is Blockchain?
Here's the elevator pitch
Let's Imagine
You (a "node") have a file of transactions on your computer (a "ledger"). Two government accountants (let's call them "miners") have the same file on theirs (so it’s "distributed").
As you make a transaction, your computer sends an e-mail to each accountant to inform them. Each accountant rushes to be the first to check whether you can afford it (and be paid their salary in "digital coins").
The first to check and validate hits “REPLY ALL”, attaching their logic for verifying the transaction (the "proof of work"). If the other accountant agrees, everyone updates their file.
This concept is enabled by "Blockchain" technology.
Example provided by Deloitte "Blockchain Explained"
You have one ledger, rather than a ledger per party.
There is no intermediary (e.g. Visa; PayPal), saving time and costs.
This would differ from parties having their own ledger, which could lead to mistakes around double entries, no entry, incorrect entries and so on. The consequences lead to disagreements - imagine goblins writing up a transaction in one ledger at Gringotts Wizarding Bank, and Ebenezer Scrooge writing up the same transaction in his own. Neither would welcome an error, nor the consequences. Though we might all pay to see that in a movie. One distributed ledger means everyone holds a shared, authoritative, single source of truth.
Blockchain is more than cryptocurrencies.