Block chain is a decentralized ledger that records all transactions across a peer-to-peer network in a way that makes the data inherently resistant to modification. It serves as an open, distributed ledger managed by a peer-to-peer network to allow for quick, safe and cheap exchange of values between two parties without powerful intermediaries. Block chain is the technology underlying cryptocurrencies like Bitcoin.

2.  Block chain is a decentralized ledger or list
of all transactions across a peer-to-peer
network.
 “Exchange of value without powerful
intermediaries"
 Technology underlying Bit coins and other
crypto currencies.

3.  Inherently resistant to modification of data.
 Serves as an open, distributed ledger for
recording transaction between two parties.
 Typically managed by peer to peer network.
 Decentralized.
 Quick, safe and cheap exchange of values.