失恋后的情感空窗期最是难熬，有人会在此伤心困顿之际，随便找一个异性来交往，以填补内心的空虚和麻醉自己。这时候的对象，就属于rebound guy/girl（备胎），其本质是“temporary lover（临时情人）”。

Rebound guy/girl is a guy/girl used on the sideline by an individual if he/she thinks his/her relationship is going to end.
“备胎”就是一个人留在身边备用以防上一段感情快要结束的暧昧男或暧昧女。
 
Rebound guy/girl would do anything for you or accompany you once you ask, for instance, having a lunch, seeing a film or going to a concert. Also, they would never go Dutch but take care of you for everything. Apart from that, they are likely to bring you gifts if they happen to be born loaded including luxury bags, laptops, jewelry as long as you are joyful.
吃午餐、看电影、听演唱会，你只要一开口，“备胎”就会为你打点一切，而且他是绝不接受你跟他们“AA制”的，因为他要照顾你的一切。除此之外，如果对方是家底丰厚的“备胎”，更会三不五时送你礼物，即使贵重如名牌包包、手提电脑、珠宝首饰，为博你一笑，就算花再多的钱都心甘情愿。

Being a rebound guy is a situation that very few men feel comfortable with. Rebound relationships cause a lot of trouble to everyone involved.
很少有男人会乐意成为女人恋情结束后的替代男。备胎的关系也会给相关的人带来不少麻烦。
 
Example:
I don't really like her; she's just my rebound girl. This rebound relationship doesn't count.
我其实不喜欢她啦，她就是个备胎而已，这段感情不算数。