Currently the voxels tag's description is this:
VOlumetric piXEL (volumetric picture element). An approach to world construction that uses small, uniform volumetric elements as opposed to the larger, non-uniform polyhedra most commonly found in contemporary games.
The term "voxels" is traditionally used to describe a volume storage type, which uses a regular grid of values, "uniform volumetric elements" is just one of the many ways to represent it (this misunderstanding probably comes from the popularity of games, such as Minecraft).
The current description excludes game with isosurface-based models or terrain, such as the whole Worms series.