At the University of Cambridge, a course is called a "Tripos." The Triposes are normally divided into Part I (sometimes IA and IB) and Part II. Part I covers the subject very broadly in the first year or two, and Part II offers more specialized options.
Visiting Students study only one subject while are at Cambridge. You'll register in one part of the Tripos related to your chosen subject and take courses appropriate to that subject. The number of courses you may take varies from Tripos to Tripos, but the overall workload of the individual Triposes is equivalent.
The Cambridge colleges will admit only those students who have taken a substantial number of courses in the subject they plan to pursue for their semester or year abroad. Your application to Cambridge includes an indication of which subject you wish to pursue, but your college will not arrange your supervisions until your arrival.
The following Triposes are available:
Anglo-Saxon, Norse, and Celtic
Archaeology and Anthropology
Engineering and Electrical & Information Science
History of Art
Modern and Medieval Languages
Social and Political Sciences
Theology and Religious Studies
Natural sciences covers a very wide range of scientific courses, including physics, chemistry, materials science, geology, physiology, experimental psychology, ecology, history and philosophy of science, molecular cell biology, plant sciences, biochemistry, pharmacology, pathology, neuroscience, and zoology. (The colleges will closely examine your background before deciding if you are eligible.)
Sciences and Engineering
Applicants to a scientific or engineering Tripos must have taken two years of university-level advanced mathematics and science courses. Mathematics is particularly important for engineering and the physical sciences; chemistry is required for most biological sciences (including experimental psychology). Students may not study psychology without a scientific background except combined with other subjects within the Social and Political Science Tripos.
Classics and Modern and Medieval Languages
If you want to study classics or modern and medieval languages, you must demonstrate advanced linguistic skill in an ancient or modern language.
Music students must have a high degree of specialist knowledge and ability. In these subjects, too, Cambridge University requires students to have taken some relevant courses in their first two years of university study.