Legislative enactments establishing arbitrary time periods in which the state must initiate criminal proceedings or not act at all are known as:

The correct answer is statutes of limitation. This term specifically refers to legislative measures that set the maximum time after an event within which legal proceedings may be initiated. If a person does not bring a claim within this designated period, they are typically barred from pursuing the claim in court. Statutes of limitation serve the purpose of ensuring timely resolution of disputes and protecting defendants from the burden of facing claims arising after a long period, which can make it difficult to gather evidence or mount a defense.

Understanding this concept is important in the context of the legal and criminal justice systems, as it delineates the boundary for filing lawsuits or pressing charges. In criminal law, the statute of limitations varies based on the nature of the crime, with more serious offenses typically allowing a longer period for prosecution compared to less severe offenses.

The other options don't pertain to the concept of time limits for initiating legal actions. Legal defenses refer to justifications or excuses that defendants use to avoid liability. Bills of attainder are legislative acts that single out individuals or groups for punishment without trial. Statutes of fraud, on the other hand, require certain types of contracts to be in writing to be enforceable. Hence, these terms do not relate to the time constraints imposed on initiating criminal proceedings.