What is the blockchain? I keep hearing about other "blockchain technologies", does this mean other cryptocurrencies or what?
The bitcoin block chain is the record of every bitcoin ever generated and every transfer of bitcoins from one party to another. Each crypto-currency that is based on the same type of technology as bitcoins has its own block chain. When people talk about other blockchains, they mean other currencies based on the same distributed currency / published transaction model (namecoin, Ixcoin, and so on).
The phrase "blockchain technology" is a reference to this model of published transactions to implement currencies with no central authority.
The Bitcoin "blockchain" is in effect the general ledger of Bitcoin. It is a recording of all transactions grouped into blocks. Each block represents approximately 10 minutes of transactions, and chaining them together has the effect of adding layer upon layer of transaction history.
Chaining blocks of transactions together by requiring a new block to reference the most recent prior block makes it harder to alter blocks in the past, since all subsequent blocks up to the current one would also have to be altered. In the Bitcoin blockchain, this is combined with a 'proof of work' that each block must include (a very large amount of work at this point), to create an unalterable history of transactions that is definitive.
New transactions can be evaluated against this general ledger with complete confidence that it is current, complete, and unalterable. With the entire blockchain publicly available, anyone can do this evaluation and prove that a transaction is valid or not.
It is likely that someone referring to "blockchain technology" is talking about any system that has this type of public general ledger.
I would suggest you to stop getting boggled by technical terms like ‘decentralized distributed ledger’.Blockchain is nothing but a long chain of blocks with transactions details recorded and new blocks added after each transaction is validated and approved.
Blockchain allows transactions to take place in a secured, transparent and decentralized manner.
When a sender transfers the information, he/she uses their private key and at the same time announces the transaction information over the network. This is when a new block is created that contains information like a digital signature, timestamp along with the receiver’s public key.
This helps all transactions over blockchain technology highly secured.