Courses normally available for credit towards a baccalaureate degree carry numbers from 200 to 599. Courses numbered below 300 are termed junior courses, those numbered 300 or higher, senior courses.
The numbering of courses at the 200, 300, 400, and 500-levels in a particular field is intended to indicate the level of sophistication involved and although many courses do not have prerequisites, it is often the case that a 200-level course is a prerequisite for a 300-level course, a 300-level course for a 400-level course, etc.