`shell` is the current shell from which you executed your `time` statement. `children` is a summary of all running processes started from (and still owned by) that shell.
`user` and `system` show the amount of CPU seconds the above processes spent in user mode and kernel mode, respectively. See https://blog.codinghorror.com/understanding-user-and-kernel-mode/ for more info.
`cpu` shows the combined values of `user` and `system`, as a percentage of total CPU time. `total` shows how long ago the shell or its oldest child process was started (here in minutes:seconds.fraction).
---
If you prepend a command with `time` (which is how it's more often used), then the shell will report time statistics only for that command:
```zsh
% time sleep 0
sleep 0 0.00s user 0.00s system 43% cpu 0.007 total
```
(`total` here is the total number of seconds it took for the command to complete.)
---
Note all of the above is for the _reserved word_ `time` in [tag:zsh]. There is also an _external command_ time on macOS, which produces slightly different output:
```zsh
% command time
% command time sleep 0
0.00 real 0.00 user 0.00 sys
% command time -p sleep 0
real 0.00
user 0.00
sys 0.00
% command time -l sleep 0
0.00 real 0.00 user 0.00 sys
585728 maximum resident set size
0 average shared memory size
0 average unshared data size
0 average unshared stack size
160 page reclaims
0 page faults
0 swaps
0 block input operations
0 block output operations
0 messages sent
0 messages received
0 signals received
0 voluntary context switches
1 involuntary context switches
2198249 instructions retired
3195521 cycles elapsed
237568 peak memory footprint
%
```
(`real` here is the same as `total`, above.)