Bitcoin – with capitalization, is used when describing the concept of Bitcoin, or the entire network itself. e.g. “I was learning about the Bitcoin protocol today.”
bitcoin – without capitalization, is used to describe bitcoins as a unit of account. e.g. “I sent ten bitcoins today.”; it is also often abbreviated BTC or XBT.
Bitcoin, the decentralized network, allows users to transact directly, peer to peer, without a middle man to manage the exchange of funds. The digital asset, bitcoin, is used like other assets in exchange for goods and services. Unlike traditional currencies and assets, bitcoin is easily portable, divisible, and irreversible. Bitcoin increases system efficiency and enables the provision of financial services at a drastically lower cost, giving users more power and freedom.