It means there are no themes or changes from the default. Most companies put different launchers or apps on there. AOSP is the default build that is pure and unchanged from what Google puts out.
Phone: LG G2
Radio: Original Stock
Galaxy Nexus LTE (Toro) with Cyanogen 11
HTC Inspire 4G with Cyanogen 7.2
Samsung Vibrant (Galaxy S) with Team Whiskey Bionix V 1.3.1
AT&T Tilt 2 (AKA Rhodium)