An Opt-In process where after a user has entered their details, they have to take a further action to confirm.
For example, after submitting an email address to receive an email newsletter, being emailed by the same company with a confirmation email that contains a link that must be clicked before you are actually on their email marketing list.
While this is an annoying system, it does lead to much better email marketing lists. By forcing a confirmation process, mistyped email addresses are automatically excluded, and bots have a much more difficult time.
Glossary Index