A term used to track the intervals at which email marketing efforts are repeated: weekly, bi-weekly, monthly, bi-monthly, etc.
Knowing the frequency of emails will help to determine how well your email list works for you. Sending emails too often can often deter leads from using your service and can lead to list member's unsubscribing from future communications. However email infrequently can have an equally damaging effect, the idea is to keep your brand at the forefront of their minds.