What is system and user in the context of CPU time? How do they differ? If an application calculates the number π, which parameter will grow?

In the context of CPU time:

• user time — the time the processor spends executing code in user space (i.e., the application's code itself).
• system time — the time the processor spends executing system calls on behalf of the application, such as input/output operations, file handling, memory management, etc.

The difference is that user time is the time spent executing user code, while system time is the time spent by the OS kernel servicing application requests.

If an application calculates the value of π, it mainly performs computations in user space, so user time will increase. System time will remain low unless there are intensive system calls.