Bitcoin is peer-to-peer cryptocurrency system that allows online transactions using a unit of exchange called Bitcoins.It came into existence in 2009.It is decentralized i.e.without any involvement of government.It can be seen as the alternative of government's flat currencies such as Us Dollars or Euros  or an alternative to the pure commodity currencies such as gold or silver coins.Each Bitcoin transaction is recorded in Blockchain .They are either mined or purchased with standard national currency. Bitcoins are kept in Bitcoin wallets which are accessed through smartphone or computer using internet.