A more thorough explanation:

The vagueness doctrine is a constitutional rule that requires criminal laws to clearly and specifically state what actions are punishable. If a criminal law is too vague, it is considered "void for vagueness." This doctrine is based on the due process clauses of the Fifth and Fourteenth Amendments of the U.S. Constitution. The purpose of the vagueness doctrine is to ensure that people have fair notice of what actions are illegal and what actions are not, and to prevent arbitrary enforcement of the laws.

For example, if a law states that it is illegal to "act in an indecent manner," this is too vague because it does not clearly define what actions are considered "indecent." On the other hand, a law that states it is illegal to "expose one's genitals in public" is more specific and less likely to be considered void for vagueness.

Another aspect of the vagueness doctrine is that a statute can also be void for vagueness if a legislature delegates too much authority to judges or administrators, which could lead to arbitrary prosecutions. For example, if a law gives judges the power to determine what actions are illegal without providing clear guidelines, this could lead to inconsistent and arbitrary enforcement of the law.

An illustrative case that demonstrates the vagueness doctrine is Skilling v. United States, 130 S.Ct. 2896 (2010). In this case, the Supreme Court found that the "honest services" statute was too vague because it did not clearly define what actions constituted a violation of the law. As a result, the Court ruled that the statute was void for vagueness.