Pumice is a rock composed of little more than the sides of tiny bubbles. It can be less dense than water. Pyroclast is a general term for a fragment of of rock ejected during an explosive eruption. Pumice is an example of a pyroclast. Tephra is a deposit of pyroclasts, that have not yet turned into a rock.
Pumice is coarse tephra, ash is fine-grained tephra.
Can be built into a tephra cone. Pyroclastic flow a mixture of ash, tephra, and other debris that flows down the mountainside. Common on stratovolcanoes where eruptions melt snow and cause landslides. Usually andesitic to dacitic in composition. Fuji, shown in fig 3.13, however, is basaltic incomposition.