Germaneness
Definition
Germaneness is the requirement that an amendment relate to the same subject as the bill it amends. The House enforces this strictly on nearly all bills. The Senate generally does not, except for appropriations bills and debate after cloture is invoked.
Why it matters
The Senate's lack of a general germaneness rule is exactly why riders can be attached there almost freely, while the House's strict rule blocks the same tactic on most bills. The same unrelated policy idea that would be ruled out of order in the House can ride through on a Senate appropriations bill.
Seen in the wild
Senate Rule XVI's germaneness requirement for appropriations bills is regularly invoked to strip non-spending riders, while the House Rules Committee routinely issues special rules waiving germaneness points of order for specific bills, effectively deciding case by case which amendments members may offer.1