Freeze-drying is a preservation method that removes moisture from food or other materials. The process involves freezing the item and then reducing the pressure around it, allowing the ice to change directly from solid to vapor in a process called sublimation. This helps retain the item's structure, flavor, and nutrients. This technique is commonly used for preserving fruits, vegetables, and even pharmaceuticals. Freeze-dried products are lightweight and have a long shelf life, making them popular for camping, emergency supplies, and space missions, where NASA often utilizes freeze-dried foods for astronauts.