Shadow reports are a method for non-government organisations (NGOs) to supplement and / or present alternative information to reports governments are required to submit under human rights treaties. Unlike governments’ reports, which often highlight the progress of the State in meeting its human rights obligations whilst downplaying violations, shadow reports often provide treaty body committees with crucial information about problems in implementation and areas of government non-compliance.
NGOs around the world use shadow reports to lobby various United Nations' bodies, including treaty-monitoring bodies, thematic groups, charter-based bodies, and the High Commissioner for Human Rights.
Source: The Advocates for Human Right’s page on Shadow Reporting.