Definition: Dimensions are ways to view and segment qualitative data in Google Analytics, used in tandem with metrics. For example, the metric bounce rate could be viewed through dimension value landing page in a report that helps ecommerce merchants understand which pages lead users to further explore their website.
While metrics measure what a user does, dimensions segment to describe who they are in the first place.
For example, Dimensions can be used to uncover the gender, age, and location of the average user. While knowing that one individual customer is from Seattle isn't particularly helpful, knowing that 87% of the company's customers come from urban areas is helpful, because people who live in urban areas have clearly defined social and financial preferences that the company can cater to.
This information could also be used to improve the company's warehouse setup (by placing warehouses closer to where customers are), reduce shipping times and costs, and possibly even allow free shipping to be offered on lower-value orders.
Furthermore, Dimensions can be used to trace the route that customers use to move through the site. Understanding the path a customer takes to get to the product they want helps explain how easy the site is to navigate, which pages are most effective at converting users into paying customers, and which pages aren't performing well enough to be worth keeping.
Constantly improving the company's online store is an important part of succeeding in ecommerce, and Dimensions can help decide what to focus the company's efforts on.
Understanding the bigger picture requires looking at data through a variety of lenses.