The three numbers represent averages over progressively longer periods of time (one, five, and fifteen minute averages).
Lower numbers are better. Higher numbers represent a problem or an overloaded machine.
Ideally you want your CPU load to remain equal to or less than the number of CPU cores in your server. So if you have a single core server a 1.0 load average will indicate almost complete utilization. If you have quad core system then a 4.0 or less load average will be ideal.
However, under Linux you can generally get away with at least 2x the core count as load average during peak times. That is because Linux is very efficient at CPU scheduling and on a web server network delays have a bigger impact than processor delays.
Additionally, load average also includes processes waiting on I/O
###As per the request at hand
It may be a good idea as suggested to add at the very least a tooltip over the display to do some very quick TLDR