Recovery window is the maximum length of time, counting backward from the current time, that a protected database can be recovered.

You must assign each protected database exactly one protection policy that determines the maximum period that Recovery Service will retain backup data to support recovery. For each protected database in a protection policy, Recovery Service attempts to ensure that the oldest backup is able to support a point-in-time recovery to any time within the specified interval (for example, the past 7 days), counting backward from the current time.