Instructions: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
Input: What did 'Four-F.' mean in the United States of the 1940s? Here is the quote from Catch-22: They had to send a guy from the draft board around to look me over. I was Four-F. I had examined myself pretty thoroughly and discovered that I was unfit for military service.
Output:
It's a classification for military service. 4-F means 'Registrant not acceptable for military service.' The context clue here you might have used to deduce an area of inquiry would be the reference to a 'draft board', which is part of the Selective Service System that determines the eligibility and thus the classification of potential draftees.