在一段感情里，除了“男朋友”和“女朋友”两种角色，有时还会出现一个有点儿惨的角色——“备胎男（女）”。
“备胎”，本意是指“给汽车准备的备用轮胎（spare tire）”；如今，在网络用语中多指一段感情中的替补、备选人，与英文流行语“back-burner guy/girl”意思相近，表示“a boy or girl of slight interest who isn't exactly qualified to date at the moment, but may come in handy later”。
- 她是你的“备胎”吧？
She’s your back-burner girl, eh? - 我其实不喜欢她，她就是个“备胎”而已，这段感情不算数。
I don't really like her. She's just my back-burner girl. This rebound relationship doesn't count. - 换上备胎
install the spare tire
