BNB is the native token of BNB Chain, formerly BSC. It pays gas on that network and is also used for fee discounts and ecosystem programs on Binance-related products.
BNB started with 200 million tokens. Programmatic burns reduce supply toward a stated target of 100 million.
Auto-Burn uses a published formula based on the quarter’s average price and on-chain activity. The amount and the transactions can be checked on chain.