Bundling is a rather odd traditional practice of wrapping a young courting couple in a bed together but bound in two separate blankets to allow intimacy without actual intercourse. The practice no longer exists in most of the world (it was also embraced by some non-Amish people, too) but is still common in the Pennsylvania Amish communities.
In some cases in the past, the girl would be bound in a sack, and her potential husband would share the same bed with her. Nowadays, the practice still exists, but it’s slightly different. They just use a bundling bed, which is a bed with a bundling board in the middle to prevent touching.