Active volcanoes are those that have erupted recently or regularly erupt, and inactive volcanoes are those that have not erupted for a long time. The exact time distinction between active and inactive volcanoes differs between experts.
Currently active volcanoes are volcanoes that are erupting presently, and there are almost always some erupting throughout the world. Active volcanoes are expected to erupt in the near future on a relatively regular schedule. Some people consider volcanoes active if they have erupted in the past 100 years, but others do not classify a volcano as inactive or dormant until hundreds or thousands of years have passed.
Dormant and inactive are often used interchangeably, but they have subtle differences. Dormant volcanoes are expected, and have the ability, to erupt in the future. They may have a long cycle between eruptions during which they are dormant. Inactive volcanoes are usually not expected to erupt in the future and have not erupted in recent history.
Dormant and inactive volcanoes can become extinct after many years. This happens when a volcano moves away from its magma source or its source becomes empty. The shifting of tectonic plates can move volcanoes away from the source, which results in extinct volcanoes that have no chance of erupting.