Wiktionary
on background
prep.phr. With the understanding that the information is not to be attributed to a specific source or quoted.
Usage examples of "on background".
Then come chapters on background, conflict and plot: theory first, then a short story, followed by a chapter on practice using the story as an illustration.
Our correspondent talked to one of these detectives on background, and he said that apparently she was assaulted in the hallway by Floyd Wayne Vishniak.
This was all on background, not for attribution, not to be quoted.