In this view, there are several numbers related to the class occupancy.  

3 | 4/8 | 5 Openings

3 (the first number) - represents how many students are expected to be in attendance that specific day, taking into consideration all enrollments and any expected absences.

4/8 - the numerator (4) represents the number of perpetual active enrollments, and the denominator (8) represents the total number of allowed enrollments in the class. There are 4 active enrollments out of 8 allowed enrollments.

5 Openings - represents the total number of openings available on that day.  This number will change depending on whether you are looking at ALL openings, REGULAR openings or TEMPORARY openings.