Okay kiddo, so the Iraq dossier is a big report that some grown-ups made a long time ago. It was about a country called Iraq that was far away from our home.
Some other grown-ups who were in charge of the country where the people who made the report lived wanted to know if Iraq had some bad things, like dangerous weapons, that could harm other people. So they made the report to try to find out.
The report had a lot of written pages and some pictures too, and it said that Iraq might have some dangerous weapons. But some people thought that maybe the report was not completely true or fair, because they didn't find any proofs that Iraq really had those weapons.
After that, some other grown-ups decided to do something about it and they sent some soldiers to Iraq to look for the weapons themselves. They searched and searched, but they couldn't find them.
So some people thought that maybe the report, or the people who wrote it, made a mistake or maybe even lied. And that's why some people still talk about the Iraq dossier today, because some people were not sure if it was true or not.