AOSP, or Android Open Source Project can best be described as vanilla Android at it sweetest.
Essentially, AOSP is a stripped down version of Google’s wildly popular mobile operating system without the bloat, flavor and skin imposed by a handset or tablet manufacturer.
Recently, Android 4.2 - the latest iteration of Jelly Bean - was pushed to the Android Open Source Project, while the SDK was updated to the 4.2 based API17.
As Haroon Q. Raja of XDA Devs notes, the update will be quickly incorporated by ROM developers, meaning the Android modder community should start seeing plenty of 4.2-based AOSP ROMs for a wide range of devices over the next few weeks.
In related OS news, Google has made the latest Android 4.2-based proprietary binaries available for a number of flagship devices, including the Galaxy Nexus, Nexus 7 and Nexus 10. Basically, this means full hardware support for the above-mentioned devices in terms of custom ROMs.