Rendition was the taking of individuals from one legal jurisdiction to another. It tended to take two forms, at least on the planet Earth in the 21st century. In many cases, it involved a perfectly legal arrest and extradition. In others, it was wholly illegal.
This latter form of rendition may have been performed when CIA agent Rex Matheson took Gwen Cooper and Captain Jack Harkness from Cardiff, Wales at gunpoint, to the United States in March 2011. He emphasised that they were not formally (in other words, legally) under arrest. (TV: The New World)