A volcano that has erupted or is currently erupting in the last 100 years is called an active volcano.

Here's why:

* Active volcanoes are defined as those that have erupted in recorded history.

* This timeframe of recorded history typically includes the last 10,000 years or more, but 100 years is a common and convenient timeframe for tracking recent volcanic activity.

* Dormant volcanoes are those that haven't erupted in recorded history but could potentially erupt in the future.

* Extinct volcanoes are those that are unlikely to erupt again.

So, if a volcano has erupted within the last 100 years, it is considered an active volcano.