Extraordinary rendition is a big fancy word that means when the United States secretly takes someone away to another country without going through normal procedures like going to court or getting permission from that person's country.
It's like pretending to play a game of hide-and-seek, but instead of just hiding in the closet, the US grabs someone and takes them to another country where they might be questioned, punished, or even tortured.
Some people say that this is very bad and not fair because people deserve to have rights and protections, while others say that it is necessary to protect the country and its people from dangerous enemies. Either way, it is a controversial topic that has been criticized and debated for years.