Traditionally, Salesforce UI design came down to two questions: Do I want to recreate the look-and-feel of Salesforce with custom Visualforce pages, or do I want to install a third party framework to create rich application interfaces?
Lighting Experience and the Lightning Component Framework solve a problem that has long been a barrier to a truly unified experience for all Salesforce users: Providing a single, integrated framework for developers that enabled the creation of rich, responsive applications that could be seamlessly “plugged in” anywhere in the UI rather than having to stand alone in separate pages or standalone applications.
What is the Lightning Component Framework?
The Lightning Component Framework was initially created to support development for the Salesforce1 mobile application, but is now the standard for responsive, client-side single page applications for the end-to-end Salesforce user and developer experience across all browsers and devices.
The framework provides a number of reusable out-of-the-box components for you to get started building your own Lightning Components, and the platform is fully maintained and supported by Salesforce.
What is Aura?
While the Lightning Component Framework and Aura have many similarities on the surface, do not try to use Aura components or functions that are not explicitly supported in the Lightning Component Framework documentation. Many developers have already found that these undocumented features may work at first, but unless they are explicitly supported by Salesforce, they can be taken away at any time.