System-arm64-ab.img.xz !!link!!

Before dissecting the name, it’s important to understand that a system image is a compressed copy of the Android operating system’s core partition. It contains the Android framework, system apps, libraries, and essential binaries—everything except the Linux kernel and vendor-specific drivers.

fastboot -w

This is arguably the most important modern feature. The "AB" refers to (also known as A/B partitioning). system-arm64-ab.img.xz