Matomo (Piwik) custom variables tracking provides a powerful & easy way to track custom values and variables about your visits (for example “Username”, “Membership level”) or page views (eg. “Category:Sport”). You can track up to 5 variables for each Visit on your website. On top of these 5 custom variables for each visit you can also track up to 5 custom variables for each page view.
Learn more about Custom Variables Analytics.