The word ‘tephra’, derived from a Greek word for ash, is a collective term for all the unconsolidated, primary pyroclastic products of a volcanic eruption. We summarise here the meanings and applicability of this and related terms, including tephrostratigraphy, tephrochronology, tephrochronometry, tephrology, and cryptotephra. These and other tephra-based terms, some of which are erroneous or unnecessary, have been used in a wide range of stratigraphic and paleoenvironmental disciplines and in archaeology.