Developing Rich Internet Applications (RIAs) for the Adobe Flash Platform.
Adobe Flex Online Training
In simple words “flex is a bunch of developer tools from adobe to build and deploy rich internet applications on the flash platform” . Flex is an adobe platform for creating rich internet applications and cross-desktop desktop applications. It is an open source framework.
Using flex we can build desktop, web and mobile applications. Flex will take care of the UI part or client-side code in web development. Flex development takes a big leap forward as Flex 4.5 release introduces multiscreen application development directly within the core Flex framework.
What you will learn
Flex creates SWF files that are rendered by Flash Player. However, Flex is primarily a developer's tool and the way you develop Flex applications is entirely different than the way you develop Flash RIAs. All Flex development is based upon a framework that provides you with reusable and extendable UI components, data retrieval services, event handling functionality and much more. You can create RIAs in a familiar code-centric environment, but you still reap the benefits of Flash applications.