$BNB was originally issued as an $ETH -20 token, running on the $ETH network, with a total supply of 200 million coins. 100 million BNB was offered in the ICO, but the current total supply is lower due to periodic burning events and a real-time burning mechanism. If you want to know more about coin burns, and why BNBs are being permanently destroyed, check out What Is a Coin Burn?.