Applies to a door where it is half open and half closed. In order to maintain sufficient airflow in an un-air conditioned room or under-air conditioned room, while still maintaining some level of privacy.
In retail closing shifts often end between 9 and midnight and opening shifts start between 7 and 9 am. A clopen is a portmanteau of closing one night and then opening the next morning, thus having as little as eight hours to eat, sleep, and shower between shifts. Depending on the kind of retail and the hours involved, clopens can be a mild annoyance or a brutal test of human endurance.
I'd love to hang out tomorrow night, but I'm clopening, so I won't get home until midnight and then need to be up at six am~