System time / wall clock time / time-of-day
System time is used to maintain the actual date and time, similar to a (perhaps rather sophisticated) watch. There are structures that contain the time passed since INtime‘s system epoch, other structures provide the absolute time and date.
The system time (aka wall clock time or time-of-day - TOD) can be synchronized with external time sources to get a common time base. Thus timestamps from different systems can be correlated.