above board是习语，意思是“光明正大的、公开(的)、开诚布公(的)、合法而坦诚(的)”。

【例句】
You don't have to hand it to him, something the talker doing isn't above board.
你们不用佩服这个演说家，他做的一些事情不够光明正大。

Don't worry，the deal was completely above board.
别担心，交易是完全合法的。