What do 'real', 'user' and 'sys' mean in the output of time(1)?

Question

$ time foo
real        0m0.003s
user        0m0.000s
sys         0m0.004s
$

What do \'real\', \'user\' and \'sys\' mean in the output of time?

Answer 1

Real shows total turn-around time for a process; while User shows the execution time for user-defined instructions and Sys is for time for executing system calls!

Real time includes the waiting time also (the waiting time for I/O etc.)