In English law during the late Medieval and early modern period (from 1321 to 1798), it was possible for Parliament to pass a "Bill Of Attainder". This declared a person guilty of a crime, often treason, by legislative act, without any trial or other legal process. See the Wikipedia article for more detail.
Often a Bill of Attainder not only decreed that a person (or people) was guilty, but also confiscated the convicted person's property, preventing his (or rarely her) heirs from inheriting, and possibly rendering those heirs ineligible to hold public offices or peerages. The heir would also be prevented from inheriting through the attainted person. For example, property held by the father of the attainted person would not pass to the child of the attainted person. This was called "corruption of the blood", and was viewed with particular horror by many during the colonial period and before. It effectivly treated the heirs of the attainted person as illegitimate.
Attainder was usually followed by execution, possibly by torture. The bill might specify the specific fate of the person attained.
The US constitutional provision prohibits declaring people guilty of crimes by legislative act, and prohibits sentences for crimes that take property or rights from the family or heirs of the convicted person, even in cases of treason. At least that is how it has been interpreted. Fines may be levied, but may only fall on the actual property of the person convicted.
The US Supreme Court has dealt with this clause in several cases:
- Ex parte Garland, 71 U.S. 333 (1866) (law requiring lawyers to swear that they had not supported the confederacy held unconstitutional);
- Cummings v. Missouri, 71 U.S. 277 (1867) (Law requiring an oath that the person had not supported the confederacy for a professional license held unconstitutional);
- Hawker v. New York, 170 U.S. 189 (1898) (a state law barring convicted felons from practicing medicine upheld);
- Dent v. West Virginia, 129 U.S. 114 (1889), (a state law newly requiring that practising physicians must have graduated from a licensed medical school upheld);
- United States v. Lovett, 328 U.S. 303 (1946) (federal law which declared three specific persons "subversive" and barred them from federal employment overturned);
- American Communications Association v. Douds, 339 U.S. 382 (1950) (federal law which required elected labour leaders to take an oath that they were not and had never been members of the Communist Party USA, and that they did not advocate violent overthrow of the U.S. government upheld);
- United States v. Brown, 381 U.S. 437 (1965) (law which made it a crime for a former communist to serve on a union's board overturned);
- and Nixon v. Administrator of General Services, 433 U.S. 425 (1977) (law seizing Nixon's presidential papers upheld).