Recurring Subscription means, when your premium membership expired, you will be automatically charged again for the next 30 days premium membership.
So you can enjoy continued access, without having to re-subscribe every month. 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 $16.95, for 30 days access.
On April 17th, you are charged another $16.95.
On May 17th, another $16.95, and so on.
Recurring payments are only for 3 days trial, 30 days and 90 days.
After you purchase a 3 day trial account, you will be automatically billed for 30-day subscription after the 3 days expire.
Premium Memberships for 365 days is one-time payments.
At any stage, you can cancel your recurring subscription. 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.