From:
http://www.seoforclients.com/hr/top/
us -> User CPU time: The time the CPU has spent running users’ processes that are not niced.
sy -> System CPU time: The time the CPU has spent running the kernel and its processes.
ni -> Nice CPU time: The time the CPU has spent running users’ proccess that have been niced.
wa -> iowait: Amount of time the CPU has been waiting for I/O to complete.
hi -> Hardware IRQ: The amount of time the CPU has been servicing hardware interrupts.
si -> Software Interrupts.: The amount of time the CPU has been servicing software interrupts.
id is idle, in other words CPU idle status
st is Time stolen from a virtual machine. Prior to Linux 2.6.11, unknown