The word 'Tripos' describes your course in Cambridge. The degree is divided into two parts. These may further subdivide eg Part I may be split into Part IA and Part IB or Part II may subdivide into Part IIA and Part IIB. In general, Part I allows students to explore a wide range of topics within their chosen field, enabling them to make informed choices about the more specialist courses in Part II. To graduate, you need to pass both Part I and Part II.