Before I even start to explain what a blockchain is, lets get some things clear first.
Blockchain is not the actual crypto asset.
Blockchain exist because OF bitcoin and bitcoin because of the blockchain.
The two are not inseparable but they can serve very different purposes.
Blockchain is not some program language or anything to do with coding in general. It is the outcome of the bitcoin protocol.
So now that we have that out of the way you should be well versed in what the blockchain is, now go out and educate other.
Oh, you want more. Fine. So what exactly is the blockchain then? If you can visualize a series of interconnected block that are increasingly growing and depended on each other then you have a general grasp.
So a blockchain is the name given to a sequence of blocks (groups of transactions) that are linked together. These blocks are then distributed to all the users on the network. If you were to download the Bitcoin Core , software that allows you to sync with the blockchain, you would immediately begin downloading the entire blockchain from the very first transaction back in 2009. Depending on your computer this can take hours or days and it is only getting bigger. Ah, but thats what makes it so cool. !0 years of every move every bitcoin has made, linked and now sitting on your computer. That's cool and one of many things that makes this technology so great.
Basically it is an "immutable record of transactions (LEDGER) that does not require to you to rely on an external authority" to validate the data. This makes it "trustless".
The thing about the blockchain is that it can contain virtually any type of data. Yes you will mostly hear about it being associated with financial transaction, but like I have said in previous posts, that is on a small part of what this thing can do.
Here is a great article on some of the uses for a bitcoin blockchain: https://www.fool.com/investing/2018/04/11/20-real-world-uses-for-blockchain-technology.aspx
Seems simple right? So how does this whole thing work?
The blockchain comes from the distribution of computers on the network, this provides the security of bitcoin. There are 5 concepts of blockchain technology:
Block Validation or ‘Mining’
The ideal hash function has three main properties:
It is extremely easy to calculate a hash for any given data.
It is extremely computationally difficult to calculate an alphanumeric text that has a given hash.
It is extremely unlikely that two slightly different messages will have the same hash. https://simple.wikipedia.org/wiki/Cryptographic_hash_function
Hashing as been around forever and this has led to many different algorithms that create different types of hash outputs.
The blockchain uses the hash function to make a unique ID for a given block. Also every block includes the Hash of the previous block, more or less. Basically it will include a segment of the previous has so the two are linked, this is why it's so secure. You can not insert your own Hash into the string because it will not be recognized and in return gets kicked out of the system.
PEER-TO-PEER (P2P) NETWORK- The blockchain information is distributed among all of the users. As I mentioned before, when you download Bitcoin Core you will get a copy of the blockchain. Now any new transaction goes through you and everyone else running the program. So the entire network can communicate and verify with each other, consensus. So even if an some attacker were to modify a part of the chain, the network will not accept it. Unless there is a 51% attack, highly unlikely and something you do not need to know right now, just beware of the term. You will see it again.
Mining is the act of meeting the Proof of Work (POW) requirements for adding a new block with pending transactions to the Blockchain. For bitcoin it is solving an extremely hard mathematical problem, these problems gradually get harder as more miners come onto the chain.
So, to sum it all up, the Blockchain allows users to create an immutable system for recording any kind of data. There is no need for an external or internal party. Users rely on the technology by following the rules to meet consensus on that protocol and thus ensuring the integrity and security of that data.