Rendition and extraordinary rendition are not terms defined by law. They describe the process by which a detainee is transferred from one state to another, outside normal legal processes (such as extradition or deportation). In many cases these detainees are transferred to secret detention or to a third country for the purposes of interrogation, often in circumstances where they face a real risk of torture.
The All-Party Parliamentary Group on Extraordinary Rendition was established by Andrew Tyrie MP (now Lord Tyrie) in December 2005, in response to allegations that the UK had been involved in the US rendition programme.
The APPG published its compendium "Account Rendered: Extraordinary Rendition and Britain’s Role” in 2011. The book contains a forensic analysis of the background to rendition, combined with a 200-page collection of primary documents, presented with commentary on their significance.