Root, Rooting or Routing is how you know the method used to give you the Administrator or Super User privileges of the Android operating system. This concept comes from OS Linux and is used in Android since, as almost everyone knows, it has a Linux base.
This Root process in Android is necessary when you need to run certain applications that need privileges from the home directory.
The rootear concept comes from English and allows applications to access parts of the operating system that are normally hidden by the manufacturer itself. This allows you to run more powerful software and install custom ROMs on the terminal that optimize the operation of your computer
Linked to the Root concept, we have the ROMs.
A ROM is an original or modified copy of the operating system/app hosted in a file. This copy can be overwritten in the terminal memory to be able to run modified operating systems or a version of the app.
On the web there are numerous listings and compilations that will help you find the ROM for your Android rooted that suits you.