The worst felony crimes, also known as serious indictable offences in the UK, include murder, manslaughter, rape, kidnapping, and armed robbery. These crimes typically involve violence or the threat of violence and are associated with long prison sentences or even life imprisonment. Additionally, crimes such as terrorism and large-scale drug trafficking are considered amongst the most severe felonies. The severity of a felony crime is determined by its impact on the victim, society, and the level of harm caused.