Plz someone tell me about Adobe Flex?

I am having confusion in Flex and Flash.
Can someone tell me about this.

Adobe Flex Builder is Adobe’s IDE for developing applications that will run in the Flash plugin. The Flex SDK refers to the libraries that developers uses to write the applications.

Essentially, the term ‘Flex’ is the development side and ‘Flash’ is the run time side of Adobe’s technology. ‘Flash’ is also used to refer to the Flash IDE which designers use.