Linux: Why the same binary shows different different output for the time comand ?

Question

I wrote and compiled c code. I am using command "time a.out" . Every time output comes different.

$time ./a.out

real 0m0.002s
user 0m0.001s
sys 0m0.001s
-bash-3.2$ time ./a.out

real 0m0.001s
user 0m0.001s
sys 0m0.001s
-bash-3.2$ time ./a.out

real 0m0.001s
user 0m0.000s
sys 0m0.001s

Can someone please explain why these different different output come ?