What is Flex?

I suppose sometimes as a Flex or Flash developer you are so immersed in the whole SWF ecosystem that occasionally you get asked a question that should be easy to answer but becomes difficult to explain to someone without a technical perspective.

The other day I was preparing a spec and getting a colleague to double check my correspondence. They brought up that the client likely did not know what Flex was and that I should be prepared to explain it to the client in the meeting we were tabled to have. My first reaction was fine until it dawned upon me that finding the words to describe flex for someone who only really understands flash as a scripting and animation technology may actually be a little difficult so thought I would share with you what I came up with as well as ask for opinions on the matter.

Here are a few possible answers:

1. Flex is a collection of compilers that output SWF bitecode
2. Flex is a framework that is based on MXML as a meta-language for forming SWF bytecode
3. The Flex framework uses both MXML and a bunch of custom Actionscript classes to define the various visual and non-visual elements of Rich Applications
4. Flex makes building Rich applications with Flash faster by leveraging the use of standard user interface components and layout method

Any other thoughts?