NeXTSTEP或NeXTSTEP/Sun取决于你问的是谁。

有一段时间，Sun在OpenStep上有相当大的投资。在Sun加入之前，基金会中的大多数东西，尽管当时还不叫基金会，前缀都是NX，代表NeXT，在Sun加入之前的某个时候，所有东西都被重命名为NS。S很可能并不代表Sun，但在Sun加入后，人们普遍认为它代表Sun，以纪念他们的参与。

实际上我有一个参考资料，但我现在找不到。如果/当我再次找到它时，我会更新这篇文章。

苹果的开发者文档如下:

Historical Note: If you’re wondering why so many of the classes you encounter have an NS prefix, it’s because of the past history of Cocoa and Cocoa Touch. Cocoa began life as the collected frameworks used to build apps for the NeXTStep operating system. When Apple purchased NeXT back in 1996, much of NeXTStep was incorporated into OS X, including the existing class names. Cocoa Touch was introduced as the iOS equivalent of Cocoa; some classes are available in both Cocoa and Cocoa Touch, though there are also a large number of classes unique to each platform. Two-letter prefixes like NS and UI (for User Interface elements on iOS) are reserved for use by Apple.

来源:使用Objective-C编程

它来自NeXTSTEP传统。

Bill Bumgarner又名@bbum，谁应该知道，他在2005年的CocoaBuilder邮件列表上写道:

Sun是在NS前缀开始发挥作用之后才进入的。NS前缀出现在从NeXTSTEP 3.0到NeXTSTEP 4.0(也称为OpenStep)的公共api中。4.0之前，a 少数符号使用NX前缀，但大多数类提供 系统库根本没有前缀——List, Hashtable， 看来,等等……

似乎每个人都同意，NX (NeXT)这个前缀在1993/1994年之前一直被使用，苹果的文档中写道:

1994年9月发布的官方OpenStep API是第一个将API分离为Foundation和Application Kit的API，并且第一个使用“NS”前缀的API。

来自Cocoa_(API)维基百科:

(重点)

Cocoa classes begin with the acronym "NS" (standing either for the NeXT-Sun creation of OpenStep, or for the original proprietary term for the OpenStep framework, NeXTSTEP): NSString, NSArray, etc. Foundation Kit, or more commonly simply Foundation, first appeared in OpenStep. On Mac OS X, it is based on Core Foundation. Foundation is a generic object-oriented library providing string and value manipulation, containers and iteration, distributed computing, run loops, and other functions that are not directly tied to the graphical user interface. The "NS" prefix, used for all classes and constants in the framework, comes from Cocoa's OPENSTEP heritage, which was jointly developed by NeXT and Sun.

当NeXT定义NextStep API(与NextStep操作系统相反)时，他们使用了前缀NX，如NXConstantString。当他们使用Sun(不要与OpenStep操作系统混淆)编写OpenStep规范时，他们使用了NS前缀，就像在NSObject中一样。