"closed-source" is not a definite license. The system is designed to err on the side of incompatibility and let the humans have the final say. Of course there are licenses which do not require all of the below, and they are still considered to be "closed source". But for combinination purposes, a license is "closed-source compatible" if all of the below are true. 1. the developer is never required to disclose source 2. the developer can require a fee is paid for every redistribution. 3. the developer is not compelled to grant patents or other license terms to anyone