A prison UPRISING, also known as a prison RIOT, is an organized protest or revolt by inmates of a prison against the prison authorities. It is usually caused by overcrowding, poor living conditions, and mistreatment of prisoners. The term 'RIOT' is used to describe a violent UPRISING, while the term 'UPRISING' is used to describe a peaceful protest. In this case, the crossword solution for the term 'prison UPRISING' is RIOT, which indicates that the UPRISING was likely a violent one.