Binance Coin (BNB) is the native coin of the Binance exchange. Its price was sitting around US$8 at the start 2018, and is looking to treble soon, having topped a new high of $24. The main reason for the sudden growth is that Binance is super popular, and frequent users can get very solid value for money with BNB. Just yesterday Binance signed up a almost a quarter of a million new users in a single hour and it's previously said it tends to grow by "a couple million" users a week.
BNB suddenly has a lot of new buyers, and you don't need to be a market guru to figure that BNB is going to be a hot commodity right now.
The coin's main application right now is alleviating the sometimes-jarring exchange fees (0.1% trading fees to hit the big spenders, and flat withdrawal fees to hit the small spenders). You can pay any Binance fees with BNB instead of another currency to get an easy 50% discount.