4fn

Could you clarify what "4fn" refers to in your request? The term is ambiguous and can be used in multiple contexts (for example as an informal shorthand meaning "for fun" in online content, or as an acronym or label for a specific project, product, or concept). If you specify the intended domain (e.g., mathematics, computing, culture, a particular organization, etc.), I can write a concise, neutral wiki-style article under 300 words. If you’d prefer, I can also provide a neutral disambiguation-style entry that surveys the main uses of "4fn" as it appears in current usage.