Our Landing Page Tagging Guide describes both the required and the recommended parameters that should be included in landing URLs for the main traffic sources.
Traffic driven from a search engine’s results page that has been paid for.
Traffic from a domain specific search engine.
This is any traffic that comes from an email.
Traffic that comes specifically from a marketing affiliate
Traffic from social networking sites, such as Facebook, Twitter and Pinterest.
Traffic from display advertising including retargeting and placement ads.
Traffic driven by offline ad campaigns such as catalogues or postal campaigns.