What is a Blockchain and why should I care? If possible; please answer in one easy to understand sentence for dumb people.
With Bitcoin; every bitcoin is recorded as a digital block, every transaction is recorded as a digital block, all these individual blocks make up the blockchain. The blockchain (or chain of blocks) keeps getting bigger and bigger as more coins are mined, and more transactions are executed.
Not one sentence. Sorry.
A blockchain is a decentralized, distributed and public digital ledger that is used to record transactions across many computers so that any involved record cannot be altered retroactively, without the alteration of all subsequent blocks. This allows the participants to verify and audit transactions independently and relatively inexpensively.
Blockchain is a “payment rail” --
A payment rail is a term used to describe a payment platform or a payment network that moves money from a payer to a payee. Either party could be a consumer or business, and both parties are able to move funds on the network. Credit card rails refer to the credit card payment system.
Blockchain is considered a newer type of payment rail.
So, to some extent, Blockchain is like inventing Credit Cards – or a new type of transaction method.
People do make money inventing stuff like that. But, as a speculative “investment”, I don’t think Bitcoin is a long-term winner. But Blockchain, as a math technique, can change the world.
When I was in the Marines, way before the Internet, I had a reputation of somebody fellow Marines could trust. It started out with some of them leaving $20 or so with me to "hold on to" so that if they got broke before payday, they could come to me to get some money. They knew that I would never steal it or try to deceive them by pretending they never gave it to me. As my reputation as a "solid guy" grew, more and more trust was given to me. They would rather give me the money to hang on to rather than put it in a bank because I could give it to them a lot faster than a bank could (this was before ATMs even).
Blockchain is sort of like building that kind of trust on the Internet. All your transactions are in a permanent database that cannot be altered. In a way, it's like doing business on eBay or Airbnb. You only want to do business with those who have high ratings - who are trustworthy.
Let's say you wanted to buy something from me for $100. You might say, why not just use cash? So we meet, I give you the item and you give me $100 in cash. What's to stop me later from claiming that I never got the cash? You might ask for a receipt but then I might claim that the receipt is fake. So you can see the kind of hassle that can be.
With blockchain, the exchange is done in bitcoin, permanently recorded and cannot be altered. Let's say you have 5 bitcoins in your ledger and I have two bitcoins in mine. So you give me 1/2 bitcoin. Now you have 4 1/2 bitcoins and I have 2.5 bitcoins in mine. The records of this are indisputable. A true peer-to-peer transaction but totally transparent. That is, thousands and thousands of computers are tracking the same transaction and recording it permanently. I will never be able to claim that you did not pay me.
Best of all, no banks or credit card companies involved (to take their piece of the action through fees).
Maybe this could be explained better but hopefully you get the general idea.