An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.
An erupting volcano is an active volcano that is having an eruption...
A dormant volcano is an active volcano that is not erupting, but supposed to erupt again.
An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.