The Subscription expiration is when your current subscription ends. License expiration is the date stamped in the license file. Initial licenses are given a one month grace period to keep the system running in case there are some delays processing the renewal and replacing the license with the updated one.

In the screenshot above, the system is expired as of 2 days ago and it can no longer receive support until the subscription is renewed. The software will continue to function until May 17th.