Opt-In is a user’s consent or action indicating they want to receive email communications.
It matters because email is one of the few channels a business can own directly. Strong email fundamentals improve trust, deliverability, segmentation, and long-term lead nurturing.
Example
A signup form explains the newsletter’s subject and frequency before a person chooses to subscribe. The business stores the consent source and keeps that choice separate from submitting an unrelated support request.