Attainder is an act passed by parliament against a person for a crime, or supposed crime, usually treason. It was a way to punish or even sentence someone to death for a crime without them actually standing trial. It was developed in the Middle Ages, and used in the Wars of the Roses by the rival houses against one another. A powerful extension of attainder was the idea of ‘corrupt blood’ which kept the heirs of the attainted person from inheriting property.
Henry VIII used attainder against, among others, Margaret Pole, Thomas Cromwell and Kathryn Howard. One presumes that he did not want Kathryn to stand trial in case potentially embarrassing details emerged while she was on the stand. Henry also used attainder posthumously against people already convicted for treason in the courts as a way of seizing property. In the reign of Elizabeth two attainders were reversed against descendents of men executed with Anne Boleyn.
The last act of attainder was used in England in the 18th century, although it was not officially abolished until 1870.