A more thorough explanation:

A Certificate of Reasonable Doubt is a legal document that is issued by a United States circuit judge in an appeal from the denial of federal habeas corpus relief. It certifies that the prisoner has shown that a constitutional right may have been denied.

For example, if a prisoner believes that their constitutional rights were violated during their trial or sentencing, they can file a petition for a writ of habeas corpus. If the petition is denied, the prisoner can appeal the decision and request a Certificate of Reasonable Doubt.

The Certificate of Reasonable Doubt is issued if the prisoner can show that the claim is at least debatable, meaning that reasonable jurists would find the claim to be valid. The prisoner does not have to prove that the case would succeed on the merits, only that there is a reasonable doubt that their constitutional rights were violated.

If the Certificate of Reasonable Doubt is not issued, the prisoner cannot appeal the decision.

Overall, the Certificate of Reasonable Doubt is an important legal tool that allows prisoners to appeal the denial of federal habeas corpus relief and seek justice for potential violations of their constitutional rights.