A while back means some time in the past.Also, a while ago. This term uses a while in the sense of "a short or moderate time," a usage dating from about 1300. Note:A while back意思是一段時間以前，過去的某個時間。也可以說a while ago。從1300年開始，while可以 代表并不長的一段時間。例：I ran into Barbara a while back but didn't get her new address. 我前陣子偶然遇見Barbara，但沒得到她的新地址。