Plus addressing (subaddressing, "+tags") means mail sent to jane+news@gmail.com is delivered to jane@gmail.com. Gmail, Outlook, iCloud, Fastmail and many others support it. Gmail also ignores dots, so j.a.n.e@gmail.com is the same inbox too.
Why it matters
People use +tags to filter mail and to see who sold their address, which is fine. But they also let one person sign up again and again with "different" addresses.
Veqen returns a canonical address for every email, with the +tag removed (and Gmail dots removed). Store it, make it unique, and duplicate accounts disappear. See stopping duplicate accounts.