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The time you use in your question is not a command, but rather a reserved word in zsh. It can be used in two different ways and its output can be customized through the $TIMEFMT parameter. There is also an external command time on macOS, which produces slightly different output.

Just time

time by itself (as shown in your question) will report time statistics for the current shell:

• 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).

time <command>

More often, time is added before a command. If you use it that way, then the shell will report time statistics only for that command:

% time sleep 0
sleep 0  0.00s user 0.00s system 43% cpu 0.007 total
% 

total here is the number of seconds it took for the command to complete.

Customizing time output

time's output can be customized by setting the $TIMEFMT parameter. For example:

% TIMEFMT='%J  %U user %S system %P cpu %*E total  %M max RSS'
% time        
shell  39.79s user 72.26s system 0% cpu 84:33:14.91 total  25848 max RSS
children  1089.58s user 919.02s system 0% cpu 84:33:14.91 total  52528 max RSS
% time sleep 0
sleep 0  0.00s user 0.00s system 61% cpu 0.003 total  580 max RSS
% 

External Command time

The external command time can be used as follows:

% 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  # Prints memory usage
        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.