Cross GNU ARM Toolchain
1) Cross - meaning you can compile on architecture A to the machine code of architecture B.
2) GNU - recursive acronym for "GNU's Not Unix!". A Linux based project focusing on providing free open source software.
3) ARM - processor core architecture. Which is the target architecture for your toolchain.  

All together - a toolchain to compile ARM programs on your (non-ARM) computer, provided by GNU.

4) There is Cross GNU ARM Toolchain for Cortex-A. And many. One of these is provided from the ARM website itself: https://developer.arm.com/open-source/gnu-toolchain/gnu-a/downloads