CPU Time Usage

I'm just wondering what exactly "CPU Time" is, I have searched Google and checked Wikipedia but still do not really understand. The main reason this is bugging me is that MySQL on our database server seems to have a very high "CPU Time" usage.

This is the top part of the output from "top", with MySQL shown:

Code:
[mike@mysql1 ~]$ top

top - 20:26:05 up 222 days, 16:14, 1 user, load average: 2.04, 2.90, 2.36
Tasks: 95 total, 1 running, 94 sleeping, 0 stopped, 0 zombie
Cpu(s): 27.1%us, 12.1%sy, 0.0%ni, 60.2%id, 0.3%wa, 0.0%hi, 0.2%si, 0.0%st
Mem: 2074276k total, 1990828k used, 83448k free, 163012k buffers
Swap: 4192956k total, 60k used, 4192896k free, 1410448k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
26826 mysql 25 0 483m 324m 5504 S 238 16.0 363300:21 mysqld
1 root 15 0 2064 592 508 S 0 0.0 0:01.24 init
2 root RT -5 0 0 0 S 0 0.0 1:13.13 migration/0
3 root 36 19 0 0 0 S 0 0.0 0:00.00 ksoftirqd/0
4 root RT -5 0 0 0 S 0 0.0 0:00.00 watchdog/0
5 root RT -5 0 0 0 S 0 0.0 0:01.17 migration/1
6 root 34 19 0 0 0 S 0 0.0 0:00.00 ksoftirqd/1
7 root RT -5 0 0 0 S 0 0.0 0:00.00 watchdog/1
8 root RT -5 0 0 0 S 0 0.0 5:34.93 migration/2
9 root 34 19 0 0 0 S 0 0.0 0:00.00 ksoftirqd/2