Recurring Subscription means, when your premium membership expired, you will be automatically charged again for the next premium membership.
So you can enjoy continued access, without having to re-subscribe. If you don't like this idea, you can cancel it in your account profile.
An example of recurring subscription is:
You join on March 17th, for $17.99, for 30 days access.
On April 17th, you are charged another $17.99.
On May 17th, another $17.99, and so on.
Recurring payments are for both 30 days and 90 days subscriptions.
You can cancel your recurring subscription at any time. You'll have access up until the next rebill date, but you won't be rebilled - your account will become free on after the last day of premium.