fall.back
n.（名词）
Something to which one can resort or retreat.退路：某人可以凭借或隐退的某物A retreat.退却Computer Science A mechanism for carrying forth programmed instructions despite malfunction or failure of the primary device.【计算机科学】 低效运行，撤退：即使主要设备失灵或产生故障也能继续按编定的指令工作的机械Something that falls back:降落物：例句：the fallback of a huge explosion.一次大爆炸的降落物
adj.（形容词）Of, relating to, or constituting a resort or place of retreat:后退的，应变的：（组成）撤退的手段或地方的，与其有关的：例句：a fallback proposal; a fallback position behind our own lines.撤退计划；在我们战线后的撤退地点
