A streak is the number of days in a row you have completed a lesson. Once you complete a lesson through the app or web, your streak will increase by 1 day. You will receive your daily reward when you meet your Daily 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!
How to equip a streak freeze
Get a streak freeze to make sure you don't lose your streak when you forget to practice for a day. A streak freeze must be purchased in advance of a day of a missed lesson to protect the streak. You can equip up to 2 streak freezes at a time.
You can purchase a streak freeze via the app and web shop.
On Web:
Click the Shop icon in the top menu.
On Android and iOS app:
Tap the Shop tab (bottom).