The term "tertiary" refers to the third level in a hierarchy or sequence. It is commonly used in various fields, such as education, where it describes tertiary education, which includes universities and colleges that provide advanced learning after secondary school. In geology, "tertiary" can refer to the Tertiary period, a division of the geological time scale that lasted from about 66 million to 2.6 million years ago. This period is significant for the development of mammals and birds, as well as the formation of modern continents and climates.