In Google Analytics, the time spent on site is called a metric which is a unit of information that tells you how your website is performing. Metrics are quantitative measures. The metric refers to a particular aspect of the website and this aspect is called a Dimension. So, time spent on site or Sessions is a Metric whereas City, Country, etc. is a Dimension.
This question is a part of the Google Digital Unlocked and Google Digital Garage Certification exams. You can find all the latest updated questions and answers to both exams on our website in the Google Digital Garage and Google Digital Unlocked pages.