What does the term "ex post facto" refer to?

The term "ex post facto" specifically relates to laws that impose penalties for actions that were legal at the time they were performed. In simpler terms, it refers to a legal principle that prohibits the government from enacting retroactive legislation that punishes individuals for conduct that was not illegal when it occurred. This principle is important because it helps ensure fairness and protects individual rights, as people should not be held accountable for actions that were lawful at the time they were taken.

In the context of the U.S. Constitution, both state and federal governments are prohibited from passing ex post facto laws, emphasizing the significance of this legal concept in maintaining a just legal system.

The other options represent various legal principles and features of government, but none specifically encapsulate the retroactive nature of ex post facto laws.