“备胎”的原意是指“给汽车准备的备用轮胎（spare tire）”。英语口语中，spare tire还常常用于表示人腰间的一圈赘肉，也就是我们说的“游泳圈”。
spare tire
an extra tyre carried in a motor vehicle for use in case of a puncture. informal a roll of fat round a person's waist.
At least the spare tire is still good.
至少备胎还是好的。
5 Ways To Lose YNcBONIbhour Spare Tyre
减掉游泳圈（腰间赘肉）的五种方法
“备胎”
如今的网络用语中，“备胎”多指一段感情中的替补、备选人，算是一段感情中有点惨的角色。“备胎”与英语流行语“back-burner guy/girl”的意思相近。
（put on the） back burner
of a l原由网ow priority; given less or little thought or attention; postponed or suspended
If you put an issue on the back burner, you leave it in order to deal with it later because you now consider it to have become less urgent or important.
Put other issues on the back burner until after the election.
其他事项搁置到选举后再考虑。
Exercise is often put on the back burner as we get older.
随着我们年龄增长，锻炼经常被置//www.58yuanyou.com之脑后。
back-burner guy/girl：
used to describe a boy or girl of slight interest who isnNcBONIbh't exactly qualified to date at the moment, but may come in handy later. thus one places them on the "back burner," keeping them warm (subtle flirting, etc.), until you're ready to chow down
简单说：the guy/gi//www.58yuanyou.comrl you strung along in case you break up with your first choice
把某人当做“备胎”可以说put soneone on the back burner。另外还有“备胎关系”back burner relationship。
她只是你的“备胎”吧？
She is juts your back-burner girl, eh?
Is he putting you on the back burner?
他是把你当做备胎吗？
‘Back-burner relationships’ are more common than you’d think.
“备胎关系”比你想象的更为普遍。
