It’s not the right term, but I found what I was looking for. Hopefully this helps you too.
setfacl -d -m group:name:rwx /path/to/your/dir
This does not work on OS X however:
-bash: setfacl: command not found
I did find this https://discussions.apple.com/thread/4805409?start=0&tstart=0
+a The +a mode parses a new ACL entry from the next argument on the commandline and inserts it into the canonical location in the ACL. If the supplied entry refers to an identity already listed, the two entries are combined.