Q: What is a “dimension” in Google Analytics?
A) A comparison of data between two date ranges.
B) An attribute of a data set that can be organized for better analysis
C) A report that offers information about your audience.
D) The total amount of revenue a business has made in a given date range.
Correct Answer is: B) An attribute of a data set that can be organized for better analysis
Dimensions are attributes of your data. For example, the dimension City indicates the city, for example, “Paris” or “New York”, from which a session originates. The dimension Page indicates the URL of a page that is viewed.
Read more here: https://support.google.com/analytics/answer/1033861