What does "Ex Post Facto" refer to?

The term "Ex Post Facto" translates from Latin to "after the fact." It refers specifically to laws that retroactively change the legal consequences or status of actions that have already been committed. This means that if an act was legal at the time it was committed, a new law could not make that act illegal and subject the person to penalty for it. The concept serves a critical role in upholding fairness and justice, ensuring that individuals are not punished for actions that were lawful at the time they occurred. This principle is enshrined in the U.S. Constitution under Article I, which prohibits ex post facto laws at both the federal and state levels. This is why the option related to changing the legality of past actions aligns with the definition of "Ex Post Facto."