What is a Germane rule?

"Germane" is an adjective meaning relevant or pertinent. It's not a specific rule, but rather a descriptor for any rule that is directly related to the topic at hand.

For example, if you were discussing the rules of a particular game, a "germane rule" would be one that actually affects how the game is played. A rule about the color of the game board would not be germane.

So, when someone talks about a "germane rule," they're simply emphasizing that the rule they're referring to is important and directly relevant to the discussion.