Diverticulosis is a condition in which there are small pouches or pockets in the wall or lining of any portion of the digestive tract. These pockets occur when the inner layer of the digestive tract pushes through weak spots in the outer layer. A single pouch is called a diverticulum. The pouches associated with diverticulosis are most often located in the lower part of the large intestine (the colon).
Metrics are numbers that tell you important information about a process under question. They tell you accurate measurements about how the process is functioning and provide base for you to suggest improvements.
1 Metrics is a number.  Dimensions is attribute of a visitor to your website : Through which campaign the visitor entered (SEO,PPC etc). Country of the visitor. How many page views and so on..