This article details the available dimensions and metrics in Google Analytics and how they're populated. To analyze data that isn't accessible in these dimensions and metrics, create custom dimensions and metrics.
Tip: Many of the dimensions and metrics come from event parameters on your site or app. To learn about each event parameter and how it impacts a dimension or metric, see Event parameters.
A dimension or metric may be grayed out when it's incompatible with other applied dimensions or metrics, or when you can't apply the dimension or metric to a selected exploration technique.
(not set) is a placeholder used when data hasn't been received for a dimension. When you send an empty value to Analytics, you will see a blank value instead of (not set); (not set) appears when no value is sent. Learn more about (not set)