Linux is often used to refer to a family of operating systems including Ubuntu, Debian, fedora, red hat, ect., which all use the Linux kernel.
However, GNU/Linux may be a better name for this family of operating systems, since they all use GNU components and (to varying extents) embrace the philosophy of the free software foundation.
Android uses the Linux kernel, but not GNU components, and do not embrace the philosophy of the Free software foundation.
Stalman, the man who founded GNU and the free software foundation published his thoughts on this: