will give you the answer:
Real time and process time
Real time is defined as time measured from some fixed point, either
from a standard point in the past (see the description of the Epoch and
calendar time below), or from some point (e.g., the start) in the life
of a process (elapsed time).
Process time is defined as the amount of CPU time used by a process.
This is sometimes divided into user and system components. User CPU
time is the time spent executing code in user mode. System CPU time is
the time spent by the kernel executing in system mode on behalf of the
process (e.g., executing system calls). The time(1) command can be
used to determine the amount of CPU time consumed during the execution
of a program. A program can determine the amount of CPU time it has
consumed using times(2), getrusage(2), or clock(3).