BNB Market = the market where BNB (Binance Coin) is traded against other cryptocurrencies or currencies.
Examples:
BNB/USDT Market – BNB traded against Tether (USDT)
BNB/BTC Market – BNB traded against Bitcoin (BTC)
BNB/ETH Market – BNB traded against Ethereum (ETH)
In simple English:
"BNB market" means the cryptocurrency trading market for BNB, where people buy and sell BNB.