Streak Rescue allows you to keep your streak alive, even if you miss a day of learning.
You can maintain a perfect streak with Rescues if you don't miss more than one day in a row. If you are a Premium learner you are given the chance to earn more Rescues and you will have to learn 5 days in a row to earn one Rescue, accumulating up to 4 Rescues for longer breaks.
The Rescues you have earned are automatically applied to your streak on the days you don't learn with Drops.