Webstore, Software subscription licenses

The product I purchased off the WebStore says it is a subscription license and will expire. What does this mean?

Subscription licenses expire annually each year. For instance, SAS licenses expire every year on 12/31. Licenses must be renewed when they expire by purchasing a new license. The U of I WebStore is able to offer software at such a discount because of the subscription licensing. A benefit of subscription licensing is that updates and upgrades that are released during the subscription period are free to active subscribers without purchasing a new license. Installation media may be required for a separate fee, however.