Okay, i am sure you heard about about software,Software is a code programming done to perform a particular task.There are various kinds of softwares categorized depending on their task,like photo editing software tasked to edit photo ,music player is a software tasked to play music.
Similarly there is software,tasked to control the all other sub softwares and hardware(like camera,speaker,screen/display,battery and it's charging) such piece of  software is OPERATING SYSTEM aka OS

ANDROID is such a software designed to control other sub softwares and hardware of your smartphone.It does this task accompanying with application firmware ,which controls sub softwares (apps) and kernal,which controls hardware (camera , sound ).

Okay the overall thing you need to take from here is, ANDROID is software which controls your smartphone.It's like neurons in brain which guides brain to perform tasks.
So next time you come across ANDROID  hope you catch exactly what it means