A rate plan charge tier is part of a subscription or an amendment to a subscription, and it comes from a product rate plan charge tier. A rate plan charge tier holds the prices for a rate plan charge. Each rate plan charge has at least one tier associated with it.
Rate plan charge tiers are sometimes called subscription rate plan charge tiers to distinguish them from product rate plan charge tiers. Rate plan charge tiers that are part of an amendment are sometimes called amendment rate plan charge tiers for the same reason. However, the object name is RatePlanChargeTier, not SubscriptionRatePlanChargeTier nor AmendmentRatePlanChargeTier: these latter two names don't exist.