A BIDH box, often used in event planning, is an acronym for "Brought In, Didn't Happen." This box is typically filled with items or materials that you brought to an event but didn't end up using. These can include various things like extra decorations, surplus promotional materials, unused name tags, spare stationery, or additional equipment. The purpose of the BIDH box is to keep track of resources that were not utilized during the event, which can help in future planning to optimize budget and reduce waste. The contents of a BIDH box can vary widely, depending on the nature and size of the event.