Which is not an example of a dimension?

Visitors" is not an example of a dimension; it is a metric. In analytics, dimensions are qualitative attributes or characteristics that describe data (e.g., "Days of the week" describes when an event occurred, "Cities" describes location, and "Devices" describes the technology used). Metrics, on the other hand, are quantitative measurements or counts (e.g., the number of visitors, page views, or conversion rates). You analyze metrics by dimensions. For instance, you might look at the number of "Visitors" (metric) from different "Cities" (dimension).