The Android Open Source Project (AOSP) is an initiative created to guide development of the Android mobile platform. The Android platform consists of the operating system (OS), middleware and integral mobile applications.
The AOSP is overseen by the Open Handset Alliance (OHA), a Google-led coalition of over 30 wireless carriers, semiconductor companies, handset manufacturers and software companies. The purpose of the OHA is to further the development of open source standards for mobile devices.
The OHA member list includes Qualcomm, Broadcom, HTC, Intel, Samsung, Motorola, Sprint, Texas Instruments and Japanese wireless carriers KDDI and NTT DoCoMo. Companies that are conspicuously absent from the OHA member list include Nokia, Symbian, Apple, RIM, Microsoft, Verizon and Cingular.
See an introduction to the Android Open Source Project: