Dimensions are elements of an Apple Search Ads campaign that can be included in custom reports, such as the campaign ID, ad group, keyword, device, or CPT bid. Dimensions will appear as rows in these custom reports. Adding relevant dimensions allows for analyzing metrics like impressions, clicks, or cost by different segments of the campaign. This provides more detailed insights than standard reports. Cross-referencing multiple dimensions, like campaign ID and device, lets users view statistics for a single campaign across different device types.