Bitcoin is an experimental new digital currency that enables instant payments to anyone, anywhere in the world. Bitcoin uses peer-to-peer technology to operate with no central authority: managing transactions and issuing money are carried out collectively by the network. Bitcoin is also the name of the open source software which enables the use of this currency.
Bitcoin is a decentralized electronic cash system using peer-to-peer networking, digital signatures and cryptographic proof to enable irreversible payments between parties without relying on trust. Payments are made in bitcoins (abbreviated BTC), a digital currency issued and transferred by the Bitcoin network. Nodes broadcast transactions to the network, which records them in a public history after validating them with a proof-of-work system.
Viewing the following short video will get you up to speed as to what is Bitcoin.