What does “Derogatory trade information on credit bureau”, mean?

I received this “reason” on a credit loan response letter.

Why not contact them and ask?

You got a black mark on your credit report, and should not only contact them, but first get a free credit report from the big 3... Experian, Transunion, and Equifax if in the US. Please note there are others outside the big 3 that are used by business to simply report good/bad stuff. Find out who put the mark on and why.

Helps if you could be aware of credit rating companies (The big 3 as referenced, and credit REPORTING agencies.