Historically an old English/Pennsylvania Dutch term for courting in the 19th century where the boy and the girl would sleep over at the parents home in the same bed supposedly without having sex (good luck with that). This was to encourage the boy to stay and marry their daughter.
A more contemporary scenario would be the acceptance by the girl's parents that their daughter is sleeping with her boyfriend in the parents home with the hope that the boy will stick around and make an honest woman of her.
Bob and Jan have committed to bundling even though their parents haven't fully accepted the idea yet.
Jan's Dad says, "Why buy the cow if you can get the milk for free." But by accepting bundling Jan's Dad knows Jan is safe and who she is with.
Bob's mom will make them have separate bedrooms. While not exactly bundling, Jan can sleep over at Bob's mom's house.
A procedure where a couple spend the night together, fully clothed, and engage in heavy petting. Common amongst the lower classes of 19th century Britain, the term still survives, alongside the practise in some rural areas, typically in the north. It has come to mean a synonym for dry sex in some parts.
"Oh, she was off bundling last night"