Piwik detects URLs tagged with Google Analytics campaign parameters. Piwik offers two dimensions for Campaign tracking: name, and keyword.
The campaign parameter (in this order: utm_campaign, or utm_medium, or utm_source) is used as the Campaign name.
The parameter utm_term is used as the Campaign keyword.
Note: you can use campaign parameters in the query string (landing?utm_campaign=PaidSearch), and Piwik also detects campaign and keyword in the hash tag string (landing.html?q=test#utm_campaign=PaidSearch)