It separates the vendor implementation from the Android OS framework via a new vendor interface. (android.gs)
The current vendor interface is so difficult that small vendors simply can't afford to participate. (news.lawreader.com)
Instead, they are moved to a separate vendor partition without having to be recompiled, and new standardized vendor interfaces (defined with HAL Interface Definition Language) allow for the OS framework to communicate with the HALs. (xda-developers.com)