Bitcoin is a crypto-currency and an electronic payment system introduced in 2008 to enable direct transactions between individuals of payments without any intermediary. Before venturing in to the world of bitcoin it is strongly recommended to read up on the cryptocurrencies' history and some high-level explanations of what it is and how it is used to complete transactions, for example watch some of the highest rated videos on bitcoin via Youtube here.
For impartial information on bitcoin, read the Wikipedia entry here.