uptime gives a one line display of the following information.
The current time, how long the system has been running, how many users
are currently logged on, and the system load averages for the past 1,
5, and 15 minutes.
This is the same information contained in the header line
displayed by w(1).
System load averages is the average number of processes that
are either in a runnable or uninterruptable state. A process in a
runnable state is either using the CPU or waiting to use the CPU. A
process in uninterruptable state is waiting for some
I/O access, eg waiting for disk. The averages are taken over
the three time intervals. Load averages are not normalized for the
number of CPUs in a system, so a load average of 1 means a single CPU
system is loaded all the time while on a 4 CPU
system it means it was idle 75% of the time.