Germaneness
A rule that an amendment must relate to the bill's subject matter. Strict germaneness rules block riders; loose rules invite Christmas trees.
Why it matters
Germaneness rules decide whether an amendment must actually relate to the bill it's amending. Strict rules keep bills coherent and block riders; loose rules turn every moving bill into a vehicle for whatever can be attached. When a germaneness challenge is raised, the presiding officer's ruling can kill an amendment on the spot, making the chair's parliamentarian one of the quietest power centers in the building.
In the game
In The Bill to Law Game's markup fights, you can challenge hostile amendments as non-germane. Win the ruling and the amendment dies without costing you a vote; lose and you've spent capital and annoyed the chair.