don't-know

A slang expression for an out trade that is used when there is a discrepancy in the details of a trade.

Also known as a "DK'd trade."

Investopedia Says:
In this kind of a trade, one of the parties "doesn't know the trade." This party either lacks information or has received inaccurate trading instructions.

Wall Street slang for a questioned trade. Brokers exchange comparison sheets to verify the details of transactions between them. Any discrepancy that turns up is called a don't know or a QT.

Securities term for a questioned trade, indicating refusal to complete a transaction due to a disagreement on the trade details or because errors are discovered in the comparison sheets exchanged by broker-dealers.

The noun has one meaning:

Meaning #1: (colloquial) a person who responds"I don't know" in public opinion poll