Zaphrentis is one of the most widely used names in Paleozoic coral paleontology. Species of "Zaphrentis" have been named from every Paleozoic System except the Cambrian. Variants of the word, such as zaphrentoid, are widely used with varied meanings. Nomenclatural spinoffs are numerous: Neozaphrentis and Heterophrentis are obvious examples, but dozens of additional genera have type species that were originally described in Zaphrentis. Many paleontologists are familiar with the word but few really know what it means. Zaphrentis (as a subgenus) and five new species were named in 1820, based on corals from the Falls of the Ohio River between Louisville, Kentucky, and Clarksville, Indiana. Descriptions were minimal, none was illustrated, and no specimens were preserved as types. Nominal species of "Zaphrentis" proliferated for over 100 years before a redescription based on Falls specimens was published (1938), the probable source beds recognized (1942), a neotype selected (1965) and adequately described and illustrated (1981). At this time, I recognize only four zaphrentid genera: Zaphrentis (middle Eifelian), Heliophyllum (middle Emsian through Givetian), Aemulophyllum (middle Emsian), and Cyathocylindrium (lower Emsian?; middle Emsian through Eifelian). All four genera seem to have originated in the Eastern Americas Biogeographic Realm. Heliophyllum is the most common, has the longest stratigraphic range, and is the only one known to occur outside of its area of origin. Heliophyllum modicum n. sp., once discussed as a possible Zaphrentis, is described and compared with both the type species of Zaphrentis and other Heliophyllum species. A single coral specimen from the Indian Cove Formation (upper Pragian or lower Emsian), Gaspe??, Quebec, is considered the earliest known zaphrentid and is described as Cyathocylindrium? n. sp.