In England, after dinner, around 8-9 o'clock we have evening tea which consists of tea and cake or biscuits etc. To help some people go to sleep they will have milk and cookies (some elderly people will have an irish coffee (has whisky inside) to keep them warm and help them sleep), that is called a bedtime snack. If during your sleep you wake up and have the munchies, we call that a midnight snack.
These are the terms as i know them from England. Not sure what other countries call them.