BTC is the currency symbol for the virtual currency, Bitcoin. 1 BTC or 0.023 BTC are some examples of how the symbol may be used.
As of January 2019, the current Bitcoin rate is about 1 BTC = $3,500.
The XBT symbol is used interchangeably with "BTC." The smallest denomination of Bitcoin is 0.00000001 BTC. This is referred to as 1 "satoshi," after the creator of Bitcoin.
The price of Bitcoin has increased dramatically since its introduction in 2009, so the value of each Bitcoin is large, making them difficult to use. To compensate for this, Bitcoin is divisible into sub-units, such as the milli-bitcoin (1mBTC = 0.001 BTC) and the micro-bitcoin (1μBTC = 0.000001 BTC).