is a placeholder of a value in a blockchain ledger. The more you pump in the digital bullion the more it worth. Plus several factors that are not so vivid as capitalization. Taking into consideration a limited emission of the bitcoins
Mined bitcoins: 16,690,400.
All bitcoins: 21,000,000.
Current market cap devided by emitted ammount equals bitcoin
135,914,600,512 / 16,690,400 = 8143$
Screenshot of the exact values: