Check out Is Android really just Linux? on Android Authority. It’s a considered, logical walk around the issues involved.

A straight forward question, it seems, but it all depends…on the meaning of your terms…

Jessica Thornsby covers how you would define Linux, then how you would define a Linux distro, and then the issue of different Androids – the Android Open Source Project (AOSP) and the role of Google Mobile Services (GMS).

She then considers the points both in favour and against considering Android as Linux.

For example:

There’s really only one argument in favor of classifying Android as Linux, but it’s a strong one: every Android smartphone or tablet contains a Linux kernel. You can even see what version of the kernel is installed on your device, by opening its ‘Settings’ app and navigating to ‘About Device > Software info.’

However, Android isn’t just the Linux kernel; it’s a fully-functioning operating system that features lots of additional libraries, a GUI, apps and much more, so when we ask “is Android Linux,” we’re actually asking “is Android a Linux distro?”

…And where does GNU or TouchWiz fit in? You’ll see.

Check it out »

What would I say? For what it’s worth, I agree with the commenters (do check out the Comments section) who opt for the formulation “Android is a Linux-based operating system”…