The peak utilization is the maximum bandwidth limit reached at any point in time on an interface whereas the average utilization provides an average bandwidth reading which gets calculated over a period of five minutes. However, the peak utilization is calculated over a 10-sec window.
The peak utilization is shown in green color on the Utilization graph whereas the average data flow is shown in blue color.
The image above clearly shows the peak and average data flow.
For Example: In the inbound traffic, the peak between 11:00 and 11:30 has reached up until 50 Mbps whereas the average data flow between that time frame is lesser as the average is calculated over a period of 5 minutes.