CommonJS，AMD和RequireJS之间的关系？

问题：

I'm still very confused about CommonJS, AMD and RequireJS. 我对CommonJS，AMD和RequireJS仍然很困惑。 Even after reading a lot. 即使阅读了很多。

I know that CommonJS (formerly ServerJS) is a group for defining some JavaScript specifications (ie modules) when the language is used outside the browser. 我知道CommonJS（以前称为ServerJS）是用于在浏览器之外使用该语言时定义一些JavaScript规范（即模块）的组。 CommonJS modules specification has some implementation like Node.js or RingoJS, right? CommonJS模块规范有一些实现，例如Node.js或RingoJS，对吗？

What's the relation between CommonJS, Asynchronous Module Definition (AMD) and RequireJS? CommonJS，异步模块定义（AMD）和RequireJS之间有什么关系？ Is RequireJS an implementation of CommonJS module definition? RequireJS是CommonJS模块定义的实现吗？ If yes, what's AMD then? 如果是，那么AMD是什么？