Literally "running around",
rumspringa is the period during which
Amish teenagers are free to experiment with
English (
i.e. non-Amish) ways of life. They get to do almost anything they want, as long as it's not
illegal, without fear of social repercussions.
The idea is that one cannot choose to be Amish without having tried out some alternative lifestyles such as using electricity, buying machine-churned butter from a 7-Eleven, and -- in one famous case -- dealing cocaine. Some Amish teens don't go particularly wild during rumspringa, and some go balls to the wall.
When an Amish teenager reaches the age of 18, they can choose to continue living as English or they can choose to officially join their Amish community and accept baptism. Most teenagers, having tried the modern way of life, choose to be Amish.