Which mobile device operating system is known for its open-source code base?

The mobile device operating system recognized for its open-source code base is Android. Android, developed by Google, is based on the Linux kernel and is designed to be customizable and adaptable by manufacturers and developers. This open-source nature allows anyone to modify and distribute versions of the Android operating system, fostering a diverse ecosystem of devices and applications. This flexibility is a key reason why many manufacturers choose Android for their smartphones and tablets, as it enables them to tailor the operating system to their hardware and user interface preferences.

In contrast, iOS is a closed-source operating system exclusively developed by Apple, which means that its code is not available for public modification or redistribution. The term "closed-source" refers to any software for which the source code is not made available to users, further emphasizing that Android's open-source model is differentiating. Lastly, iCloud is a cloud storage and cloud computing service from Apple, not an operating system at all; hence, it does not relate to the question about mobile operating systems.