Although the terms membership and subscription can, and are often used interchangeably, we try to make an important distinction:

Memberships are the pricing package that you have available on your site. For example, "Gold Membership", "Silver Membership" etc. Memberships can have the status of Published or Unpublished.

A subscription is the series of payments FOR a membership according to the payment "terms". e.g. "19.95 USD for 30 days, then 19.95 USD every 30 days". A subscription can have three different statuses, Active, Cancelled, or Expired.
​Read more on statuses here.