Android is a mobile operating system that uses a custom Linux kernel. You can imagine a kernel as the brain of an operating system. The type of kernel used in an OS determines what type of OS it is. Linux flavors use a Linux kernel, Windows editions use the Windows NT kernel, iOS and macOS use Apple's XNU kernel (XNU itself is based on Unix). Easy right?
Android is a mobile operating system based on a modified version of the Linux kernel and other open-source software, designed primarily for touchscreen mobile devices such as smartphones and tablets. Android is developed by a consortium of developers known as the Open Handset Alliance, though its most widely used version is primarily developed by Google. It was unveiled in November 2007, with the first commercial Android device, the HTC Dream, being launched in September 2008.
At its core, the operating system is known as Android Open Source Project (AOSP) and is free and open-source software (FOSS) primarily licensed under the Apache License. However most devices run on the proprietary Android version developed by Google, which ship with additional proprietary closed-source software pre-installed, most notably Google Mobile Services (GMS) which includes core apps such as Google Chrome, the digital distribution platform Google Play, and the associated Google Play Services development platform. While AOSP is free, the "Android" name and logo are trademarks of Google, which imposes standards to restrict the use of Android branding by "uncertified" devices outside their ecosystem.Over 70 percent of smartphones based on Android Open Source Project run Google's ecosystem (which is known as simply Android), some with vendor-customized user interfaces and software suites, such as TouchWiz and later One UI by Samsung and HTC Sense. Competing ecosystems and forks of AOSP include Fire OS (developed by Amazon), ColorOS by OPPO, OriginOS by Vivo, MagicUI by Honor, or custom ROMs such as LineageOS.
The source code has been used to