Source to segment results by. This parameter must not be sent with any other segmentation parameters, i.e. any parameters in [browser, device, attribute_id, attribute_value].
Campaign: Contains users that arrive on a URL containing a 'utm_campaign,' 'utm_source,' 'gclid,' or 'otm_source' query parameter. If the URL contains one of these parameters, the visitor will count as "Campaign" traffic even if they arrived through search.
Direct: Includes all users who do not have any external referrer in their URL.
Referral: Includes all users that come from another URL that doesn't count as Campaign.