What determines a monitor’s resolution?

Resolution.

The resolution of the monitor refers to the maximum amount of pixels that can be displayed on the screen.

HD is a common standard referred to by television manufacturers which now generally use 1080p, as resolution that is made up by a horizontal display of 1920 pixels and a vertical display of 1080 pixels.

Is an OS system software or application software?

If we think of the computer system as a layered model, the system software is the interface between the hardware and user applications. The operating system (OS) is the best-known example of system software. The OS manages all the other programs in a computer.