A streak is the number of days in a row you have completed a lesson. Once you complete a lesson in the app or via web, your streak will increase by 1 day. You will receive your daily reward when you met you XP goal. Your goal is set when you create your Duolingo account, and can be changed by accessing: https://www.duolingo.com/settings/coach
It is represented by a little fire or flame icon. If you have not met your streak, it will be greyed out. It will become lit once you have met your streak by completing your daily lesson.
Keep your streak going and see how high you can go! Get a streak freeze to make sure you don't lose your streak when you forget to practice for a day. Check back often to make sure it is equipped, as the streak freeze only works once.
You can purchase a streak freeze via the app and web shop.
Tap the Shop icon.
On Android and iOS app:
Tap the Shop tab (bottom).
*Please note that some mobile users who have lingots will need to tap on their lingot total to access the shop.