The term "Isagoge" refers to an introductory text or guide, particularly in the context of philosophy and logic. It is most famously associated with the work of the ancient philosopher Porphyry, who wrote a commentary on Aristotle's categories. This work served as a foundational text for students of philosophy, providing essential concepts and terminology. In the Middle Ages, "Isagoge" became a crucial part of the curriculum in universities, influencing the study of logic and metaphysics. It helped scholars understand the classification of beings and the nature of universals, shaping the development of medieval philosophy and the works of later thinkers like Thomas Aquinas.