Course Numbering System at McGill
The first four characters of a McGill course number refer to the unit offering the course. For example, MSE courses begin with the Subject Code ENVR.
The three numbers following the Subject Code refer to the course itself, with 200-level courses usually taken by U1 students, 300-level by U2 students, and 400-level by U3 students. As a senior undergraduate student, you can also take some 500-level courses, but you should limit yourself to no more than one per term. For more information, see Programs, Courses and University Regulations > University Regulations and Resources > Undergraduate > Registration > Course Information and Regulations.