1. If the serial interface is not able to generate an interrupt, set this value to any unused interrupt vector address. 如果串行接口是无法产生一个中断，将此值设置为任何未使用的中断向量地址。
2. The Garbage Collector does an excellent job of managing memory for you, and it removes unused objects in a very efficient manner. 垃圾收集器在管理内存方面为你做了卓越的工作，它以非常高效的方式移除未使用的对象。
3. Pave the way for employers to allow workers to convert their unused vacation or other similar leave into additional retirement savings. 为雇主允许其雇员将未用的休假或者其他类似的福利转换为额外的退休储蓄而铺平道路。
英英解释
adj.
1. not yet used or soiled
2. not yet put into use
3. not in active use
4. infrequently exposed to
