Variable Open is a type of setup where the exact distribution of roles is randomly chosen from a public list of possibilities.
The F11 setup is an example of a Variable Open game. In F11, the actual setup can be any one of four different possibilities chosen at random. However, all four of those setups are known in advance.
Contrast Open Setup, where the exact distribution of roles is the same every time.
Because the exact distribution of roles can be determined in a predictable way, Variable Open games are considered Open enough for mafiascum.net's Central Park.