A penalty is the sanctioning of a website by Google. The reason for punishing a website is because of a non-compliance with the Google Webmaster Guidelines.
Lily Ray explains Google manual actions, or penalties
Types of Google Penalties
Google penalties come in two flavours, manual– as well as algorithmic-penalties.
Both kinds of penalties have almost the same effect on a sanctioned website:
- Ranking positions fall massively
- The Visibility Index takes a massive hit