BTCB is a BEP2 token that is 100% backed by Bitcoin (BTC). The reserve addresses are published for anyone to audit.
A trading pair will be created on Binance.com between the pegged token and the native coin, e.g., BTCB/BTC. Large buy orders will be maintained on the trading pair on Binance.com, with a price spread of around 0.1%. This provides a way for anyone to convert from the pegged token back into the native coin on Binance.com. If this buy order is filled, a new order will be placed while an equal amount of funds will be deposited from the reserve address into Binance.com. The sum of the buy order and the funds on the published reserve address will be bigger than the total supply of the pegged token, which would theoretically ensure 100% backing.