Blockchains are incredibly popular nowadays.
what is a blockchain?

as the name indicates, a blockchain is a chain of blocks that contain information.

this technique was originally described in 1991 by a group of researchers.

then it was originally intended to timestamp digital documents so that it’s not possible to back them or to tamper with them. almost like a notary.

however, it went by mostly unused until it was adapted by Satoshi Nakamoto in 2009 to create the digital cryptocurrency bitcoin.

a blockchain is distributed ledger that is completely open to anyone.

they have an interesting property

once some data has been recorded inside a blockchain, it becomes very difficult to change it.
find step by step knowledge about blockchain here:- http://blogparagon.com/what-is-blockchain/