Unwanted tags are a broad way of tagging clicks that is used for unwanted clicking patterns that do not necessarily indicate click fraud. These are usually reserved for:
clicks coming outside of targeted geographical area(s)
repeated clicks from display placements with no or low on-site interaction
repetitive clicks that are not converting
How to tag clicks as unwanted?
You can opt-in to tag clicks as "unwanted" in your Advanced Rules. If you are using Simple Rules some clicks will be automatically tagged as "unwanted".
Learn more about click tags here.