To put it briefly, it is a type of computer program which is designed to run a computer’s hardware and operate the application program. The best example for the system software is the computer OS (Operating system) such as Windows and macOS.
In addition to that, the device drivers which to control specific hardware or devices that connected to the computer, and the software tools to help the user to perform system maintenance of their desktop or laptop.
These are the most basic level of your computer, and it allows you to operated the operating system to interact with the hardware. It is a software that runs in the background and used to be accessed by the programmer instead of the end-user.