It means that your charging habits are bad for the battery life. You probably keep it too long hanging on the charger, after it has been charged.
So it means that my battery is degraded ?
Use 3rd party battery apps to check. Play store is full of those. But I don't think you did something "serious" to damage it. This is more like a warning that you should pay attention to your charging habits.
In accubattery app you can set the warning beep at a given percentage of battery charge. So you can never overstress the battery.
Battery care shows you how you charge your phone.
The above scenario shows you might be keeping the phone plugged in even after the battery has reached 100%.
You can use schedule charging mentioned in the screenshot, Using time schedule the battery will accordingly charge & a you can use it for overnight charging.
It is for those who don't keep a track on charging patterns & you should always keep a tab when battery reaches 100%.
It means you don't charge properly your phone!