Bitcoin is a digital currency. Bitcoin is a revolution. Bitcoin is financial freedom. Bitcoin is so many things...but, when you take a step back, Bitcoin is just a new form of peer-to-peer networking, which creates Bitcoin's blockchain via "mining", and a new protocol.
For a more detailed analysis, check out our article on "What is Bitcoin?" It was written some time ago, so I may need to go through it again soon, to make sure it is up to date, but it should give you a good start.