A block chain is a transaction database shared by all nodes participating in a system. Block chain technology was popularised by the cryptographic currency Bitcoin.
With regard tot he Future of the Federation, blockchain technology can enable various forms of innovative Governance of the Commons.
The Blockchain is usually referred to as an Open Ledger maintained by the nodes in a Distributed Network. Each network node stores its own full copy of the block chain.
From Bitcoin by Analogy 
Approximately six times per hour, a new group of accepted transactions, a block, is created, added to the block chain, and quickly published to all nodes.
Apart from financial transactions it as a number of applications. See Block Chain Projects.
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The mechanics of a bitcoin transaction block chain, which is a construct that is generated by bitcoin miners and functions as a global ledger for recording and validating bitcoins - khanacademy.org
For many people Bitcoin is the Blockchain. However is more accurate to see Bitcoin as a specific use of blockchain technology.
The Blockchain is usually referred to as an Open Ledger maintained by the nodes in a Distributed Network. Each network node stores its own full copy of the block chain.
Here I collect some examples of projects using Block Chain Technology.
A proof-of-work (POW) system (or Protocol, or Function) is an economic measure to deter Denial of Service Attacks and other service abuses such as Spam on a network by requiring some work from the service requester, usually meaning processing time by a computer.
In the case of cryptocurrency Proof-of-stake is a method of securing a network and achieving distributed consensus through requesting users to show ownership of a certain amount of currency.
A blockchain is a peer to peer tool that works something like an open ledger. Every participant in a certain network had access to the whole history of every "transaction"- whether it be financial as in the case of Bitcoin, or also general information.