Something/activity that used to be very popular in the past but not anymore

I agree with Alice's answer, but just want to clarify something. There used to be two kinds of "drive-ins" in the US: the drive-in movies that Alice mentioned, where you sat in your car and watched a movie projected on a giant screen in front of you (and all of the other people in other cars); and drive-in restaurants, where you sat in your car while waitresses took your order and then brought your food out for you to eat in your car. The drive-in restaurants were the kind that sometimes had roller-skating waitresses.

@Rachel, you’re very welcome.

@Alice Thanks a lot. Your answer is pretty understanding and helpful!

Hi Rachel, "all the rage" means it was very popular "back then' means at that time In your examples it means that it was popular to marry a Targaryen during that time period, and that during the time period in the past drive-ins with roller-skating waitresses were popular. If you are not sure what 'drive-ins' refers to it means a movie that you can watch while you are parked in your car. Hope that helps, Alice