The word "tertiary" typically refers to something that is third in order, level, or importance. It is often used in contexts like education, where it describes higher education or college-level studies following primary and secondary education. In other fields, it can denote classification or hierarchies, such as in geology (tertiary period) or in health care (tertiary care, which is specialized medical care).
The term "tertiary" comes from the Latin word "tertiarius," derived from "tertius," which means "third." The word has been used in English since the late 15th century.