MAME4droid is released under a dual-license (GPL / MAME license) of your choice. Under the GPL license in addition you have some extra rights granted by a special license exception which allow you to link the MAME4iOS & MAME4droid GPL source with the not GPL MAME source.
The exception also gives you the rights to eliminate it if you don't like it or if you want to include the MAME4droid source in another GPL program. So, MAME4droid is 100% GPL.
You can more easily think at it as a sort of double license. A GPL or a GPL + exception. You have all the rights of the GPL, and, if you want, some others.
The only limitation is for MAME4droid. MAME4droid cannot include external GPL source without the explicit permission of the source copyright holder.
Copyright © 1997-2015, Nicola Salmoria and the MAME team. All rights reserved.
Redistribution and use of this code or any derivative works are permitted provided
that the following conditions are met:
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
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AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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