The term "tertiary" generally refers to the third level in a hierarchy or sequence. In education, it describes post-secondary institutions, such as universities and colleges, where students pursue advanced studies after completing secondary education. Tertiary education often leads to degrees, diplomas, or certificates in various fields. In geology, "tertiary" refers to a specific period in the Earth's history, known as the Tertiary Period, which lasted from about 66 million to 2.6 million years ago. This era is significant for the development of mammals and birds, as well as the formation of modern landscapes and ecosystems.