This is a custom falling threshold configured for one specific resource user's or group's usage of a resource owner sub-type, falling back to the resource-owner-sub-type's default value if a rising threshold was configured but this falling value was left unset. This matters because leaving the falling threshold unconfigured does not mean no falling threshold -- it silently inherits a sub-type-specific default, so an admin auditing a custom threshold policy needs to check whether this value was explicitly set or just defaulted. An admin who sets only a custom 50 percent rising threshold on the BGP Router process without an explicit falling value would get whatever default falling threshold applies to processor memory generally, which might not be the hysteresis gap the admin actually intended.