After some serious search, I found this article which gives satisfactory explanation on Load average.
A simple version of the above given article is given in this URL:
For people who don’t have time to go through these articles, here is the summary:
“The point of perfect utilization, meaning that the CPUs are always busy and, yet, no process ever waits for one, is the average matching the number of CPUs. If there are four CPUs on a machine and the reported one-minute load average is 4.00, the machine has been utilizing its processors perfectly for the last 60 seconds. This understanding can be extrapolated to the 5- and 15-minute averages.”