How to understand the output of time command?

From: http://zch051383471952.blogspot.com/2010/01/different-of-real-user-sys-time.html

Real refers to actual elapsed time;
User and Sys refer to CPU time used
only by the process.

• Real is wall clock time – time from start to finish of the call. This is
  all elapsed time including time slices
  used by other processes and time the
  process spends blocked (for example if
  it is waiting for I/O to complete).
• User is the amount of CPU time spent in user-mode code (outside the
  kernel) within the process. This is
  only actual CPU time used in executing
  the process. Other processes and time
  the process spends blocked do not
  count towards this figure.
• Sys is the amount of CPU time spent in the kernel within the process. This
  means executing CPU time spent in
  system calls within the kernel, as
  opposed to library code, which is
  still running in user-space. Like
  ‘user’, this is only CPU time used by
  the process.