Bitcoin is a P2P digital currency that is these things:

• Standard currency of the Deep Web
• P2P cryptocurrency
• Mined using a process similar to Folding@Home - Bitcoin mines by making calculations while Folding@Home solves protein folding problems.
• A high-risk investment
• A experiment on digital currencies, not readily accepted yet
• Has a parody called Dogecoin
• Extremely liquid
• Neither a "standard" nor fiat currency
• Secure
• Lacks a physical representation

Basically, Bitcoin is a currency that is backed by mining and protected by encryption.

I don't use Bitcoin personally.