At the end of the course registration period you will have a few days to register for open spots in classes that are not yet full. In general, this option is available mostly for classes offered by the Faculty of Social Sciences, Economics and Business. You can find a link listing all available class spots in KUSSS News after all course allocations have been made.
The allocation procedure for open spots is on a "first come, first serve" basis.

See also: "How Are Classes Allocated?"