Badges are awarded to encourage and incentivize positive community actions within the site
Badges (along with reputation) are what makes Stack Exchange sites tick.
If you have a question about how the badge system works, or a question about a specific badge, this is the tag to use.
Want to know more?
Visit the Badges page for a list of available badges.
The FAQ: List of all badges with full descriptions, provides an intensive information regarding each badge, how it gets awarded, and exactly what it means.
Reference: imported excerpt and adapted wiki from the main Meta stack Exchange site.