https://www.nytimes.com/2017/05/15/business/all-about-bitcoin-the-mysterious-digital-currency.html?ref=business&_r=0
Bitcoin (B is capitalized) is the token, and bitcoin (b is lowercased) is the network.
Bitcoin is the e money that can be used to exchange real world currencies without revealing the users' identification. When it was created in 2009, there were only 21 million coins available. Now, the Bitcoin market is just like stock market, you can buy and sell online. The price of Bitcoin fluctuates. It goes as high as $1,800 for one coin. Partly because of its decentralized network and the blockchain (the global ledger where all Bitcoin transactions are recorded), the corporate world also has interest in the technology that enables Bitcoin. Banks are betting that real world banking one day will be run on networks similar to bitcoin that moves money more quickly, efficiently and securely.
It is so unbelievable that Silk Road is the name of online drug markets!!! where Bitcoin is popular.