Android is a mobile operating system (OS) currently developed by the on-line company Google (famous for the Google Search Engine, Google Earth and Google Maps) based on the Linux kernel and designed primarily for touchscreen mobile devices such as smartphones and tablets.
At the time of writing, Android is the most distributed OS for tablet PCs and mobile phones.
If what you require from a tablet or phone is access to the Internet, access to social media and the ability to watch video, listen to music and play games Android is probably ideal for you. At the time of writing Android is not well supported when it comes to Office type applications or creative software.
As Android is based on the Linux Kernel and the Linux Kernel is a Unix-like OS it is much more difficult for criminals to create viruses and Mal-wear for this OS and that, coupled with the fact that Android is not as prominent as Windows, means that there are, at the time of writing, no such hazards at large to worry users.